To me a visitor pass should be for anyone who is there to do a job for the company/airport that does not involve the operation of the aircraft. eg: electrician, plumber etc.
If it is being used by people emplolyed to do a job for an airline eg: baggage handling or check in, then I would imamgine that is outside the regulations
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You would imagine wrong.
Perhaps they shouldn't have named it a visitors pass. A visitors pass is issued to people who need access to the secure area (and also check-in staff etc), who don't have a valid asic. They may not have a valid asic for a number of reasons including being an actual visitor, but also if their current asic has expired, they've left it at home, they've lost it, it hasn't been issued yet etc. They will need to be supervised by a valid asic holder.
Aerocare, like QF and the myriad of other companies working at an airport may from time to time have staff with visitors pass. It's nothing unusual and is not considered a security issue.