I don't believe this is ever referenced in the books, so by default I would say RAW is use the stat block of the beast just as written in the MM, but this is one of those times I would probably be a nice DM and rule that since magic summoned them the natural attacks count as magic. Afterall I think all summons are spirits or outsiders just in the form of animals not animals in that world teleported to your side away from their dens and such.
I can most definitely see many DM's saying to just use the rules in the monster entry which then would be no, and that is more than OK. So if you are running the game whatever your gut says go with it, if you are playing ask your DM.