I would say no risk of tennis elbow at all.The elbows are usually static.After a lot of playing the shoulder blade muscles ache a bit,but that is where the power comes from to push the bellows in and out.Even this action can be reduced by the type of instrument you play.An English and Duet for example requires very litte bellows movement,normal playing requiring smooth flow of air with very little in out playing that the Anglo requires.Certain techniques may require this action as you progress with the instrument but there is very little if no strain at all on the elbows.
Al