If you're curious if the mob in your group is conventional, i.e. they take away exp when you're grouped, then they'll have NPC next to their name when you use the group command. Conventional likely includes bears and tamed animals of the beastmaster class. You can tell if they add exp, as in a groupmate bonus, because they'll have * by the NPC, again while using the group command.

None of them work like Conjurer pets. The only mobs in the game that work like them are Nightwalkers, as far as I know. Meaning, they're not part of your group but they're treated as if you kill the mob/pc, if they get the final hit, and do not affect the group exp bonus.