or is Axl making him wear it so most casual fans will think that it's Brain.? ?
I don't think many casual fans know who Brain is.
They probably think Adler or Sorum is still drumming.
I wouldn't be surprised if he is wearing it because of the smoke machines. I'm told that continually breathing in that stuff makes you lose your voice temporarily. You know when you go to a concert and you stand really close to the front etc. and the next day you struggle to talk properly. Well I always thought I lost my voice due to the yelling and singing - whilst I am sure this doesn't help, I have been told that the smoke machines contribute a fair bit to it too. I have a mate that used to work security in nightclubs and he said the smoke machines were a killer for your throat.
And yes I know that Frank doesn't do a lot of singing - but I'm sure the guy still likes to be able to talk the next day.