
They should definitely be fine. As long as you teach dobe to play gently, there'll be no problems - if you don't, you end up with a dobe like mine, who merrily thumps small dogs with his front paws to try and make them play!! He does this a lot to my sister's chihuahua, and poor little Monkey ain't happy about it.
Do make sure you teach him that when the little dogs have had enough, it means they've had enough - Remy will back off from an older dog he's annoying, but when Monkey growls or snaps (when he's really pissed) he doesn't take him seriously. Of course, Remy is one of those dogs who will generally ignore what everyone wants unless it suits him otherwise :D or unless you have food!