Well let's look at this logically.
Overlord is a seven or more foot tall giant of a man in heavy armor, wielding a heavy sword/axe/mace that can cast destructive magic.
His minions are vicious trolls/gremlins that can equip heavy armor and wield swords, axes, claws. etc., some can cast magic, some can revive other Minions, and some are super 1337 ninja assassin's.
Olimar, going by scale, would be about a three foot tall fat guy in a space suit, who controls small onion people, with the only ones being relevant in this scenario are the purple and red ones.
Yeah I say Overlord can take on a good portion of the army himself by setting the little vegetable men on fire.