I'm not sure what you're reading, but ulx_users.lua is no longer used.
If you'r using ulx v1.13 (latest for v1) ... see gmod9/lua/ulx/configs/users.ini
If you're using ULX v2, which requires Ulib>1, see gmod9/lua/Ulib/users.ini
(Though files named same, the access requires different setup, make sure to read/pay attention to detail)