OK, sorry for all the updates, but I solved it so I might as well paste the solution for anyone who might be stupid like me in the future.
default decal for terran is decal_terran01_01.dds. If you take the decal and color the alpha channel black, it makes it transparent. I'm sure most of this is obvious to most people.
Update again: Apparently you can replace Raynor's Raider's but you no matter what decals I replace, default (terran) and the default texture remains with the same logo. I have no idea where it gets it from since I replaced all the ones like that.