Since all domestic rabbits are the same species, they can breed with each other.
When you mix 2 different breeds, there is no telling what you will end up with. The rex fur is a recessive gene, so a first generation mix would not have rex fur. Manes on lionheads might show up in a cross, but even purebreds might not have a good mane. Personalities vary so much with rabbits, even within a breed, that there is really no telling what the rabbits will behave like. Some traits can be genetic, but many are how the rabbit is raised. So overall, you would probably end up with a rabbits that are about 3-5 pounds, with normal fur, possibably a mane and who knows what with personality.
It is really not a good idea to breed mixed breed rabbits with no purpose in mind. Usually when breeders mix breeds, they are looking to improve or introduce a trait. It is done carefully and takes many generations to breed true again. There are really too many mixed breed pet rabbits looking for homes to breed more.