I'm not saying make an entire area. I am talking about a small area such as a corner or ledge area designed to act as a retreat area. It would not need to even be permanent or anything. It could even be one of those toy hay houses designed for rabbits to do into. You are testing to see what the rabbit does. If when the rabbit is chased by the cat, it retreats to this type of area, you need to take action to condition either the cat, the rabbit, or both.
It sounds like the rabbit is probably fine with what is happening. But by doing this, you can get a better answer to your original question. Heck, you could even use simple markers such as breathing, ear position, what direction the rabbit faces, the sounds you can only hear when paying close attention, and display of the eye whites to determine if this causes distress.
It's also worth noting that, if the rabbit is a relatively new addition, don't be surprised if he or she humps the cat. Even when spayed or neutered, they will still do it as it is a behavioral thing. If a rabbit decides a certain area is his or her territory, they will hump the crap out of dogs and cats. My current rabbit is a spayed female and, being free roaming and having decided that the entire home is hers, she will hump visiting animals to, presumably, send the message that, "this is MY area."