You can give different permissions to different users, but it's always either one aux or all auxes, which makes sense because a musicans controls one aux and a monitor mixer controls several auxes.
Check the manuals for more information:
Consoles: StudioLive_Series_III_OwnersManual_V6_EN_10062019, section 9.4.2 "Permissions"
Rack Mixers = UC Surface: UC_Surface_ReferenceManual_EN_04042019, section 9.1.1 "Device Permissions"
You find the manuals in the download area of the mixers.