Putting 151 custom models would be way to huge for a multiplayer map (if not using them in singleplayer campaigns). So you need to use Blizzards models to make them look similar to some of the available Pokémons.
Suggestions:
Purple teamcoloured Wisp -> Gastly
Purple tinted Voidwalker -> Haunter
Phoenix -> Moltres
Red tinted Wolf -> Growlithe and Arcanine
Skeleton (tinted?) -> Mewtwo
Dark tinted Stormaul Ogre (or any other fat units) -> Snorlax
Yellow tinted Raccoon (or Rat) -> Pikachu
Rock Golem -> Geodude, Graveller and Golem
Blue tinted Rabbit - Nidoran (female)
Pink tinted Rabbit - Nidoran (male)
Seal -> Seel and Dewgong
Lich or Banshee Ghost (red tinted?) -> Jynx (?)
Yellow tinted Grunt -> Electabuzz (?)
However, maybe you can find some custom models here that looks similar to some of the Pokémons.
