Thralls dancers of level 3 or greater could know to play the drums already in the game. It would be a way of delivering “tribal music” in percussion style and would be a clever way to diversify the function of a group of dancers. Incidentally, if the current drums have a purely “decorative” utility, now they would be functional as well. Oh, and within its area of effect - which could be similar to or greater than that of dance - all allied attacks could get a bonus. Or even there could be different types of “music”… even to increase the class of armor for example. Or even the joint use of musicians and dancers could offer greater benefits to allies.
The simple fact of music helping morale in the troop is a realistic and functional example of how to motivate our soldiers to be more efficient.