Probably a bit late for you, must might be useful for anyone else that has the issue and finds this thread -
I just had this exact same problem after buying a new headset (Mad Catz F.R.E.Q 7). It worked in everything except Arma 3 (although that's the only Steam MP game, so it probably wouldn't have worked in others), and as I found out after reading a couple of forums posts, I also found it didn't work in Steam (and Steam is the problem).
I had to unplug the headset, restart the PC, installed the headset AND the drivers (even if windows installs the drivers automatically, install them manually as well).
Once I did that the mic was recognised by Steam and worked in Arma 3.
