A dog and cat could mate and have sex together.
However a dog cannot get a cat pregnant and a cat cannot get a dog pregnant.
I remember one time as a kid my male dog had sex with my female cat and I thought that there would be part cat and part dog babies from the cat.
The cat never got pregnant because my dad assured me that it's impossible for the dog to get the cat pregnant or vise versa.
For the animals to get pregnant they have to be of the same species.
So cats cannot get pregnant by dogs and dogs cannot get pregnant by cats and thankful for that because that would be really weird.