I'm sure they do. I hope so anyway. One of my professors is sexy as hell! I'm sure regardless of age they still notice which of their students are attractive. Or, if the student is under 18 or something, they probably notice how "cute" or "adorable" they are. When it comes to university I'm sure the lecturers do find at least one student attractive, whether or not they act upon it. Seeing as there are so many students in one class and only one professor, I'm pretty sure that the chances of a teacher finding even one student attractive is high.
Yes. A person notices if a person is attractive regardless of anything. It would just be wrong if the student is under 18 and the teacher is having sexual thoughts about the student. That's crossing the line.