Firstly, I understand what matter are the regulations from my own college and advice from my supervisor. I would like to ask this question more as a survey of experience and opinions.
It happens that my supervisor has suggested an external examiner that has lead a lab for numerous years, with extensive experience, knowledge and publications in the field of my thesis, who would surely be suitable in examining the quality of research work by expertise, but also one who comes from a research institute that does not use the titles "Lecturers" or "Professors".
According to the written regulations, an equivalent or higher rank is required, without specifying the nature of origin institute. As I search for more information to understand more of the general practice, I saw some writing "universities or research institutes", while oftentimes this is not specified.
It would be nice if anyone could share more on what have you seen and been thinking so far. Thank you so much!