Since a standard tactical light mount will not fit the M9, can the M9 be modified with a Dremel to accept the standard (Glock/Picatinney) holders?
No - there was a thread about this the other day. IIRC, you would have to remove more material than is on the frame to get to the picatinny specs... All you can hope to accomplish is to make your M look like an A1. Sell the M and get the A1 if it's that important to you - I prefer the A1, personally...
I'm not sure it's real important, more idle curiosity at the moment. I've never trained with a flashlight mounted on the pistol, but I can definately see the advantage.... Thank you.