[Ogedei]

I would suspect if you used them all the time, you would develop poor form.

I never used paddles, but I don't own any, not because I have anything against them.

I did do the opposite drills, ie fist drills, which obviously are trying to accomplish something else.

As ODB mentioned though, the rotator cuff already gets a lot of work when you swim, so make sure you are doing exercises to strength them out of the water as well.