Somehow or another Caribou will be dragged into the fight. Do you think he will stick with the SH side or go with Dekker?
For me he still is just the first task on FI to show some of Luffys new Haki skills which Luffy will later use fully in the fight vs the main villain of the arc(hopely a fishman).
Caribou being a logia seems perfectly fitting for a first villain Luffy has to use Haki against,
but Caribou showed so many differnet facettes of his chara that i wouldn`t be surprised if he stays a bit longer in the story planning something and after he is reunited with his crew he makes his move, instead of just being used as a 0-8-15 fodder pirate being beaten in minutes.
That is not the way Oda handles a logia.
So yeah, him joining for a while Decker is possible, but i think he will always work just for his own goals non the less.