I think if they worked like the Pokemon trainer it'd be good. Max fights while Sam shouts "Sic 'em, little buddy!" from the sidelines, and pressing B would make him shoot. Then maybe the DeSoto could be their final smash, as Sam drives around while Max shoots from the roof.
Here's my idea for a moveset:
B: Sam shoots
>B: Max uses the boxing glove
vB: Max uses his Ocean Chimp God powers to absorb projectiles. Or something.
^B: Sam throws Max into the air "Whee!"
Final Smash: DeSoto
Taunt 1: "You crack me up, little buddy."
Taunt 2: "Shall we trash the place, Sam?" "Can't think of a reason not to!"
Taunt 3: "Holy (different exclamation each time)"
Bluster Blaster and Bosco could make good Assist Trophies too.
And if they can't use guns, there's always the tear gas grenade launcher.