Is it okay to add a lecturer on LinkedIn
I do not believe an educator would feel they were put in an uncomfortable position by a student sending a LinkedIn request. 

You should not, however, expect that the lecturer will accept your request. Some lecturers like to be very close to their students. Personally, I like to keep a professional distance from my students, even after they graduate. Of course, if a student happens to share a common area of research as me and wants to work together, that would be different but I certainly do not accept many requests to "connect" to students, even after they graduate.

What you should avoid is sending multiple requests or following up in person "Hey, did you get my 'quest? It would be super-kul if you'd add me." If they want to connect they will. If not, they will just consider you a student who is interested in having a closer connection than they want and they will ignore it.

Either way, I do not believe any lecturer would be made uncomfortable by your gesture of interest.