no your puppy is not showing dominance. don't worry about that.
humping is rarely a dominance thing. dogs humps for a NUMBER of reasons generally related to being "over aroused" (not sexually, just energy-wise). Especially for puppies. If you don't want the pup humping toys or your other dog just interrupt and redirect to another activity.
Even the term "bully" is possibly inaccurate in this case. puppies are a a handful and "in your face". especially if the dog doesn't correct them. It's just how they can be, doesn't make them a bully or aggressive or dominant.