There is some circumstantial evidence against the claim that most people who publish with predatory publishers are aware that they are not publishing with a regular scientific publisher.

1. Many authors of papers published in predatory journals are inexperienced with academic publication. From [1]:

The majority of authors who publish in predatory journals have no other publications, whereas the second largest group consists of authors with fewer than five journal publications elsewhere; very few authors have published more than 10 articles. In contrast, the histogram reveals that group 2 authors, those who publish in OA journals that have a robust review process and subsequently rejected Bohannon's false submission, generally have a stronger publication record. With the exception of a few new authors, most group 2 authors have published journal articles previously; in fact, some authors have published more than 30 articles.

(Group 1 journals are open access journals with low-quality or no peer review; group 2 journals are open access journals that have more rigorous peer review process than the journals in group 1. All are biomedical science journals.)

2. Many prospective authors are unfamiliar with predatory journals and unaware of predatory practices in the academic publishing industry.

In a survey of 145 medical and veterinary science participants in a scientific writing workshop [2]:

Thirty-four of 142 (23.9%) respondents were aware of the DOAJ; 7/143 (4.8%) were aware of Beall’s list, 33/143 (23.0%) were aware of the term “predatory journal”, and 24/142 (16.9%) were aware of the Science article about predatory journals.

In another (very small) survey of U.S.-based authors who published in criminal justice journals on Beall's list [3]:

Just under half (44%; 4 respondents) of the respondents had heard of the “Scholarly Open Access List” and one-third of the respondents had heard of the term “Predatory Journal.” Furthermore, all but one of the respondents was not aware that they had published an article in a journal associated with the predatory journal list. One respondent questioned the accuracy of their association with a predatory journal, and stated

… should not be on the list. They had more referees than any other journal I’ve pursued and I’m [the] author of 20 peer reviewed papers (sic).

References:

[1]: Xia J, Harmon JL, Connolly KG, Donnelly RM, Anderson MR, Howard HA. Who publishes in “predatory” journals?. Journal of the Association for Information Science and Technology. 2015 Jul 1;66(7):1406-17. DOI: 10.1002/asi.23265

[2]: Christopher MM, Young KM. Awareness of “Predatory” open-access journals among prospective veterinary and medical authors attending scientific writing workshops. Frontiers in Veterinary Science. 2015;2. DOI: 10.3389/fvets.2015.00022

[3]: Noga-Styron KE, Olivero JM, Britto S. Predatory Journals in the Criminal Justices Sciences: Getting our Cite on the Target. Journal of Criminal Justice Education. 2016 Jul 8:1-8. DOI: 10.1080/10511253.2016.1195421

There is some circumstantial evidence against the claim that most people who publish with predatory publishers are aware that they are not publishing with a regular scientific publisher.

1. Many authors of papers published in predatory journals are inexperienced with academic publication. From [1]:

The majority of authors who publish in predatory journals have no other publications, whereas the second largest group consists of authors with fewer than five journal publications elsewhere; very few authors have published more than 10 articles. In contrast, the histogram reveals that group 2 authors, those who publish in OA journals that have a robust review process and subsequently rejected Bohannon's false submission, generally have a stronger publication record. With the exception of a few new authors, most group 2 authors have published journal articles previously; in fact, some authors have published more than 30 articles.

(Group-1 journals are open-access journals with low-quality or no peer review; group-2 journals are open-access journals that have more rigorous peer-review process than the journals in group 1. All are biomedical-science journals.)

2. Many prospective authors are unfamiliar with predatory journals and unaware of predatory practices in the academic publishing industry.

In a survey of 145 medical and veterinary science participants in a scientific writing workshop [2]:

Thirty-four of 142 (23.9%) respondents were aware of the DOAJ; 7/143 (4.8%) were aware of Beall’s list, 33/143 (23.0%) were aware of the term “predatory journal”, and 24/142 (16.9%) were aware of the Science article about predatory journals.

In another (very small) survey of U.S.-based authors who published in criminal-justice journals on Beall’s list [3]:

Just under half (44%; 4 respondents) of the respondents had heard of the “Scholarly Open Access List” and one-third of the respondents had heard of the term “Predatory Journal.” Furthermore, all but one of the respondents was not aware that they had published an article in a journal associated with the predatory journal list. One respondent questioned the accuracy of their association with a predatory journal, and stated

… should not be on the list. They had more referees than any other journal I’ve pursued and I’m [the] author of 20 peer reviewed papers (sic).

References:

[1]: Xia J, Harmon JL, Connolly KG, Donnelly RM, Anderson MR, Howard HA. Who publishes in “predatory” journals?. Journal of the Association for Information Science and Technology. 2015 Jul 1;66(7):1406-17. DOI: 10.1002/asi.23265

[2]: Christopher MM, Young KM. Awareness of “Predatory” open-access journals among prospective veterinary and medical authors attending scientific writing workshops. Frontiers in Veterinary Science. 2015;2. DOI: 10.3389/fvets.2015.00022

[3]: Noga-Styron KE, Olivero JM, Britto S. Predatory Journals in the Criminal Justices Sciences: Getting our Cite on the Target. Journal of Criminal Justice Education. 2016 Jul 8:1-8. DOI: 10.1080/10511253.2016.1195421