Paige,
I think you should train with this guy until you lose your frustrations. When you train with an uncooperative uke he doesn't learn anything but you can learn a lot. You win, he lose.
I think that generally it's a good idea to train kihon in go-tai and when you train awaze to do it in ju-tai. That is, uke loosen up as you focus more on timeing and flow, and resist when you're focusing on form. But what do I know, I'm only 3rd kyu.
Also I believe your sensei thought you wanted help with *your* technique when you called for him. Everytime I can't do a technique on a resisting uke I call on the instructor and ask what *I'm* doing wrong. If I'm lucky he shows me a different variant or an applied form of the same technique.
Good luck with your training.