Everyone does it. Take characters/people and either give a Pokémon team or make them Pokémon themselves .
It started with the obvious Kecleon and eheh 'evolved' from there. Making the desert animals ground/rock/steel types just made sense. If they can survive the move sandstorm then they're pretty well adapted right?
Beans was a little tricky but she kinda looks like a Marowak. The triangular face, getting over the death of a parent. Though she doesn't carry his remains, that jar of ashes counts. Plus that bone club could be an analogue for her shotgun
Of course Jake is a Steelix. It's called the dosh garn "iron snake pokémon" And he's a shiny since he's more gold than silver, also he gets to be special like that. :P
I picture them in a sort of Mystery Dungeon setting. Its pretty much exactly the same as the movie except Pokémon

Rango - Kecleon (normal) : Colour Change (façade, swagger, trick room, recover)
Beans - Marowak (normal) : Battle Armour (endure, outrage, boneclub, fire punch)
Jake - Steelix (shiny) : Sheer Force (fire fang, iron tail, bind, taunt)