You can see in other critters that different species can be friends. Mine even take care of each other. ZaZa the cat is about 16 now and a little cranky. The other cats don't want to walk passed her. If one of the dogs see what is going on they will walk between the two cats to stop the tension.
When my Lucy dog was young she did not come when I called her. Ashka and Fancy cat both went after her to smack her and make her come back to me.
I don't know how they understand each other but two of anything can bond.





