Rainbow 6 and Rainbow 6: Rogue Spear are both Classic applications... they might work under classic, but I doubt it. Somebody may have ported them, but again, I doubt it. I don't know for sure though, so don't lose all hope.
R6 and R6:RS will both run just fine on older hardware in 9, if you have it. I ran them both just fine with my G4 400 with Rage 128 Pro (16 MB). I'd say an old iMac (333 perhaps... probably lower, too) could handle the original R6 just fine, at least, based on what I remember from my 400 doing with Rogue Spear.