Yep, Barney is the security guard you control in Blue Shift and can be easily spotted in Half-Life throughout the game. There's also another security guard named "Otis", who can be spotted in Blue Shift.
I don't know if Valve will ever think about putting those guys(Otis & Sheppard) back in HL2 as cameo appearances or possibly in a future expansion pack(i.e. Opposite Force 2 & Blue Shift 2) It would be neat though to see their face being lifted in the Half-Life 2 engine(aka "Source Engine") like they did with G-Man(so life like! He's one creepy guy) and Barney. This comment was edited on Apr 24, 22:43.