Moulton, those settings are set at server startup within /cfg/server.cfg, a non ULX file part of every Source server.
I believe Gmod may also have another 'defaults' file somewhere, but I don't remember for sure.
ULX just allows for changing them during the game, and isn't made to save the settings.
There has just actually been discussion within the XGUI release on whether or not to complicate ULX even more by including saving/restoring those type of settings at startup.
