Do universities allow you to submit letter of recs from elective teachers? Would it make a difference if I didn’t ask from a core subject teacher?
It depends upon the college. Most that want recommendation letter want them from an academic subject. What subject did you have with this teacher?
I had PE with this teacher.
That wouldn’t be a good idea.
If it’s an optional additional letter of rec that shows some side of you the other recs didn’t address, it’s ok. If you use it to replace one of the core recs then it will look bad; colleges will assume you couldn’t find one of those core teachers to write a supportive rec.