The problem with TCAS in environments for which it was never initially intended, is that 'nuisance alerts' may cause pilots to assume that the device is crying wolf. Don't forget that the original idea was to protect airliners from ATC incompetence...
When evolving AAR SOPs for the A310MRTT, we discussed TCAS at length. During transits to an AARA, it would be normal to select TA/RA for best protection. But outside controlled airspace with VFR traffic nearby, crews needed to be aware that they may receive RAs prompted by GA traffic going about its business, so we suggested that TA would be preferable. In AARAs, TCAS TA would warn of approaching receivers, which was no bad thing, but RA was pointless - it would require pilots either to ignore it, risking a culture of ignoring TCAS, or follow the RA pursued by the receiver trying to join formation! So we agreed that TCAS went to TA only in the Before Tanking checklist and went back to TA/RA in the After Tanking checklist.
If the Hawk ACT sorties are flown in segregated airspace, then why not put TCAS to Standby when entering and back to TA after leaving? Otherwise nuisance alerts risk developing a culture of ignoring TCAS advisory alerts, which could one day prove fatal.
A bit like the GPWS warning for Avianca flight 011, which the pilot ignored for 15 sec mumbling "Bueno, bueno" until his Boeing 747 collided with the terrain, killing 181 of the 192 people on board.
There's no point in any alerting system unless it is used only within an environment where it will work correctly, with pilots responding instinctively to genuine warnings.