As has been discussed before, the M1943 uniform worn by US infantry in Korea was in use in WWII, but only in Europe, I believe, and only from autumn of 1944, and even then sporadically. This means that figures equipped in the M1941 Parsons jacket - as most are - are incorrect for Korea. The only currently available figures in the correct uniform, as far as I'm aware, are the Empress range. The old Wargames Factory plastic figures had the later uniform, but have not been reissued by Warlord, though it would seem likely that they will be at some point.
With regard to the Warlord US plastic infantry set, the box reads: "These G.I.s could be painted as late war French (post D-Day) or even Brazilians fighting in Italy!" This is the second Warlord release of US WWII infantry. On the earlier box, it was stated - incorrectly - that they could also be used for Korea. This was presumably before the Warlord honchos decided on a Korea supplement for the Korean War, and started doing some research.