I'm pretty sure you can't get DeHackEd to work with gmDoom (atleast right now), even if you manage to patch a DeHackEd p-wad into it (because the gmDoom "engine" is addon-dependant, so the only way to get DeHackEd "running" in it would require modification of the addon). D4T isn't going to work either (right now, both because of the reason DeHackEd won't and the fact it requires Decorate), since it's a .pk3 mod. All of this could change if the dev added support for them, though.