I tested it by pakrating vgui textures from a map that I downloaded from the database and named the map sp_a27_test (A27 is the loading screen name from the map I downloaded). So I deleted the files once I published it to test it, and it showed black. Can someone explain to me why the workshop or pakrat didn't like what I tried out?

Yeah, you can't have custom loading screens on the shop.

The reason is the game needs to have the textures loaded before the loading screens start. With pakrat, both load at the same time so it doesn't work out, unforutnetly.

OK. (It's weird that you need VMTs for loading screens. They're not in game materials).