I am an undergraduate student wanting to transfer to another institution for undergraduate studies. I am a research assistant for a professor at an institution that I do not attend.
Would the university which I which to transfer to, accept the recommendation letter from this professor? Again, I have not taken any courses with this professor, nor go to the institution where he teaches.
Related (except for Graduate Admissions): Copied Letter of Recommendation?
The point of a letter of recommendation is for the receiving party to obtain third-party verification that you are, indeed, awesome. Generally speaking, people like to receive letters from individuals who know you well professionally. In most cases, teachers cannot write good letters, as they only know you as a face in the class, and never really got to know your work ethic, personality, and capabilities. A research advisor would be able to comment on all those things, and would be able to write a much stronger letter.
In general. the criterion for a letter of recommendation is not "someone whose course you've taken.__ In general, the letter of recommendation is supposed to be written by someone who knows you well, and can testify to your strengths and weaknesses.
Unless there's a specific demand for a letter from someone who has taught you, you should not worry about the fact that your research advisor hasn't taught you. In principle, because a research advisor has worked more closely with you than a typical instructor would, your should expect to get a more useful letter from the research advisor, as OBu indicates.
The general answer is: "It depends on their rules regarding the admission process".
If they accept (or require) letters of recommendation, and they don't explicitely relate it to teaching relationships, they will take such recommendation letters into acount (and I personally would rate them even higher than a standard "this guy has great grades"-letter).
