Yes! All promo pets, and 48 pets can make hybrids if mixed with either of what I just said.
Only the exclusive promo pets the pets that come from a real world promotion and there is no other way to get those pets. If you use mix two of those you will get another kind of pet. Level 48 pets only have a small chance of making a hybred when mixed with each other.
If you mix anything with the more common pets you will have a very high chance of getting the common type pet.