Though it's been many years since I ran a gmod server, I'm pretty sure;
1) the file is "server.cfg", not "server.config", though, there are command line options to use different config files at startup.
2) it's "sv_noclip 0", not "sbox_noclip 0"
3) Even if I'm wrong about #2, that's what setting 0 on the server does, disables for all but those with ULX access to noclip.
4) DarkRP very likely has it's own controls for noclip - we don't know though.
5) Moving this thread, as it's more a general Gmod/DarkRP than it is for ULX (we can move back if it comes back to discussion regarding much ULX help)