You can always try asking. There is no incentive for them, but it has been known. however mining leases are usually fairly small, and equipment may move around them with little prior notice, even in areas not apparently being mined. They can have other reasons for saying no than simply a desire to prevent you getting any gold (eg conditions of their public liability insurance, and their responsibility to protect the public on a mining lease - Victoria has only just now introduced the new law of "Workplace Manslaughter", with gaol terms). For example an "inactive" area might be designated for future waste rock disposal, everyone employed on site knows and has OH&S training, a prospector no one realised was there has a truckload of gravel dumped on him.....
Easier to confine your prospecting to Exploration Licence areas - no permission required from holder (although other government restrictions can apply), no liability to the exploration holder....and little chance of having rock dumped on you.