We have guinea pigs and rabbits and they all have intermingled. The rabbits for the most part ignore the cavies only giving an occasional nudge. The cavies clearly want to be friends with the rabbits, but don't seem to mind if the rabbits pay attention or not.
As far as housing goes, one of our guinea pigs resides with our Jr Doe mini rex. It is not something that is recommended, but we had to make a last resort housing decision. Brownie was brought home from a rabbit show to be buddies with Mr Squeekies. Well, that didnt work out at all as Mr Squeekies bullied Brownie. I didn't have another cage to put poor brownie in, so I put him in with SunDancer. He cuddled right up to her and she didn't mind a wink. SInce then, they have been together, but this is just a temporary situation as I expect the rabbit to start getting territorial as she matures. But for now, its working. I see them sitting side by side snuggling each other every morning and eating hay together. She has even been caught grooming him. He does he eat her pellets, but I make sure he eats most of his diet the proper guinea pig food, and he gets kale and bell pepper pieces for his Vitamin C requirements.
This being said, its not permanent situation, and I would not normally house them together. I DEFINATELY would not house someone else's cavies with your rabbit. It's not worth the risk when it comes to someone else's pets.