Question: What do the drummers do? It says they increase moral. What does moral equate to in attack/speed for affected soldiers? Seems like it makes them faster, but not 100% sure. What would be the best use for them?

Answer: 
What I actuall discovered is that upgrading also inproves his effect. first level gives about 10-15% boost for damage, and third level about 30%, however this is distracted from critical hits. The fist-rule I use is, if a drummer can boost at least 4 soldiers, or 2 soldiers and 1 hightened soldier, of if you heighten the drummer itself it can boost 6 soldiers, then I choose to build the drummer
The Drummer can increase the morale of soldiers with 30 or 40 percent. And when it upgrade to the third stage, it can covers more soliders.