Drummers were vitally important to maintaining cohesion and issuing orders in linear combat. The noise and smoke were constant. If you want to have an idea of what it was like, go outside and light off some fireworks. Then take a metal rod and bang it around inside a metal pipe. Now multiply that by ten thousand.

Drums and horns weren't just decorative showpieces, they were vital instruments for officers to issue orders, set marching pace and otherwise communicate.

To answer your question, musicians generally only carried armament for personal defense and would generally only use it if attacked.