So, after some digging this is what I’ve found out. The game definitely uses your game mode, but it doesn’t use some elements within the game mode. Rather, these elements are overwritten when you play the game, and there’s nothing you can do about it. The HUD, and the camera are perfect examples.
In your game mode you can define a HUD, but it will do nothing. So, I had to go ahead and change the core HUD. Once I did that, it worked fine. This is kinda crappy, and I’d way rather have my own version (in fact I’ll still keep a copy). Devs, can we look at fixing this?