Not true. Some mules are fertile and other mammal species are known to produce fertile hybrid offspring. See my post below.
:can a Jungle CarpetXGreen Tree reproduce with other of the same
To my knowledge no F2's have been produced from this hybrid. Until that happens the best answer is that we don't know. Even if we knew they had the same chromosome number we cannot say for sure that this will cause infertility in hybrid offspring.
But if I were to bet I'd say that they will be fertile.