As has been stated by the people before me, it doesn very much depend on the people involved; their writing styles, expectations and motivation for the roleplay. I've seen it executed brilliantly and horribly, but even if it's done right it doesn't always guarantee success for the roleplay. In my experience roleplays generally need character development of some degree for it to have longevity because then people become invested and feel like they're part of the roleplay themselves. But it isn't impossible to develop characters while there is action going on; just because your character undertaking action, doesn't mean they can't still be feeling. 

I guess in that vein action can be very much a strong engine for driving character development as it shows their natural instinct and base feelings without so much conscious thought as say a social conversation. But it very much does depend on the people involved and even then the chemistry of how it works with all the writers.