I took a short look on it.. it manly made the maps darker and removes a few weather effects (which you can remove in the normal settings anyway). I don't see any advantage if someone use it. Probably you will heat up your CPU a bit more which is a + in winter. Btw: If you have the hardware UT2k4 can run in 4K as well.
It's another rendering mode, so yes AntiTCC know which mode you are using. It should not be a problem here, but may on other servers.
I was just wondering tbh, I use it in other games and it is a huge improvement in clarity and colour saturation.
Don't think it will do much for this game, just don't want to get banned for testing it out.
For example I use this in playerunknowbattlegrounds, without reshade everthing is just one blurry haze with little to no color, but I also think it's more for the more recent games that tends to blur and postprocess everything to a smudge.