I've got a dog that can indeed be used as a "slot" (thanks to the config info posted up earlier), but there's problems in having a team member who is a dog. For one, the dog doesn't always follow the group, and sometimes will not follow an order (like "move there" etc). Also the dog will report enemy units and will try to talk to you.
Thinking about it, dogs are not team members, the dog handler is the team member, and he has a dog as a "tool" that he uses. To this end, I think I'm going to implement it this way, have the dog as a tool the handler uses, but the handler is the team member.