When launching the server you can add a +gamemode "GAMEMODE NAME"
In your SRCDS.exe or your .bat file there should be a code familliar with this:
C:\srcds\orangebox\srcds.exe -console -game garrysmod +gamemode terrortown +map gm_flatgrass -maxplayers 24
As you see i added a "+gamemode terrortown" which makes my server, use a gamemode.
So edit either the srcds.exe shortcut, the batch file, or what file you use to startup your server.
I use a shortcut.
In this shortcut, i typed the startup command
As you see, it says -gamemode terrortown, and thats the gamemode command, as you've probobly noticed, which will start up your server with a specified gamemode.
If you don't know what your gamemode is called you can look under garrysmod/gamemodes - And there you have it
Your code should be:
(SRCDS LOCATION) -console -game garrysmod +gamemode ultimatechimerahunt
And then your own details as a server name etc.
If this doesn't work, you should contact the author for permission and support as loopyman metioned.
- I hope this helped!
//LouieTien