Is not very explained, but they believe that it can happen with the beast races as well. Khajiit are especial in my opinion, since they have a large veriety of forms. They focus on the Cathay, Suthay and Ohmes ones that are more humanoid. The Morphology of those types of khajiit are unknow to me. But i read that they are a cat/mer mix to them. For Example, a female Cathay Khajiit can have a sexual system very similar to a human or mer female, with the exception of some minor aspects like behaviour that are more like a normal female cat will react thats why she can end up pregnant from another race (It could be wrong or true). Is most theories in these stuff since are not very explained in the lore. It is explained that argonians lay eggs. How can a human or mer pregnant a female argonian is beyond me. Generally TES lore is very fascinating (And sometimes contradictory).