The US Marine Corps did not participate in SOG Ground Operations; the USMC did Participate in SOG Air Operations and there were some Marine Personnel in SOG Headquarters. See  MARINE AIR ASSETS

It is said that there was one Marine who went out on a patrol with a recon team??

USMC and FOB3, Khe Sahn 1968/69.

Dear Mr. Noe,
I was directed to your SOG site by a fellow Marine. I found it most interesting, as my unit (Combined Action Co. Oscar) had the pleasure of living and working with some of your comrades at FOB 3 in 1968.
After the initial assault on Khe Sanh village, Combined Action Company Oscar and other American units were withdrawn to the Khe Sanh Combat Base. However, the Marine command, perhaps fearing enemy agents, refused entry to our Bru counterparts. Fortunately for all concerned, the command of Special Forces Forward Operating Base 3 were glad to get our Bru, as they recruited Bru "strikers" from the same tribe we did for their CIDG units. They were so happy to get more Bru, they were even willing to take the Marines! As a result, we fought and worked alongside them for the duration of the Siege, and occasionally ran patrols and outposts for them. In a few instances, we participated as volunteers in their operations.
I thought some of your members would be interested in some of the material on my site, particularly in the "In Memoriam" section, which commemorates some of your comrades whom we served with. I am sure that you may know some of them -- the late MSG Bill Wood and his team (most of whom were KIA on 471), Harlan E. ("Rip") Van Winkle and his team, and others, including Lee Dunlap. (In fact, I think your name seems familiar. I seem to remember it having been mentioned by some of those gents -- -- or did we perhaps meet at a SOAR in Vegas? I attended some in the '90s as a guest of Rip, Gren, Lee, and Bulldog.)
In any case, here is the site:
The SF / SOG info begins about 1/2 way down the page, under the heading:
Army Special Forces Ambush and Rescue Operations on Hill 471, 29 January, 1968

If you think your comrades would be interested in this material, please feel free to link to it or otherwise disseminate it to them. These events have also been published elsewhere in various publications (albeit in varying forms of accuracy), including the late Harve Saal's SOG (V. III). (Sadly, Harve published his work before certain information became available to him, so some of his details of Bill Wood's ambush and our foray on 471 are not entirely accurate.)
Semper Fidelis,

F. J. Taylor
USMC (Ret.)

CAP Oscar-2
Khe Sanh, RVN, 1967-8