Its my understanding they carry whatever they want/can on a personal basis, or sometimes on a team basis.
I believe Strider's (Mick S. and Duane D. customs too), Emerson customs, Randalls, ATC 'hawks, and other, similar, higher-end, higher-quality, "high speed low drag" cutting tools are rather popular with the Special Forces crowd.
If any special forces member carried an Al Mar I'd expect it to be the Warrior design, and to have been a few years back. the current SERE fixed blade looks nice and has gotten really favourable reviews... so maybe its gaining some attention from the SF crowd, but I wouldnt know.
But like I said, no "Issue Knife" for the Special Forces as far as I know... if there is, its likely its the same as might be issued to other soldiers, which I guess would be the M9 bayo or a Ka-bar style thing.