If I have worlds with homeworld universities installed, is it possible to have my sims attend university there by travelling there and enrolling there, rather than using the UL university world? Would be nice to have some variety in the uni my young adult sims attend that way

I have never played a Homeworld University. But I think this should work, subject to comments from others who have tried it. You may need to adjust a couple of things after arrival such as setting Treat as Vacation to False or pausing the travel clock (either should be undone before returning home) to account for a 2-week stay if that is preferred over the shorter 1-week Uni terms, and because sims who are on a vacation do not by default go to work/school.

If not though, I suppose you could always move the sims there "permanently" but not really permanently and move them back once finished. There there would be no vacation mode getting in the way.