If there's fighting, it really really wouldn't hurt. Both for medics on scene (in the worst case scenario Bil would be secured so much faster for quick escape and Chopper's light enough in Brain point to come along with him) and a assist for Law, because the guy will need to rest at some point.

And it would also reassure the other SHs too, and yes, be more plausible.

And Chopper and Law working in tagteam is canon and this should happen for that reason too