I would be concerned with the fact QF have a spare A330 lying around to send on search and rescue missions, or was it waiting to go into the paint shop to be put in JQ livery???
I would have no concern at all.
Legacy carriers, as opposed to low cost will often have the flexibility within their flying & maintanence schedule to allow additional adhoc flying.
That adhoc may be SAR, as seen here. Charter to their own LCC, or additional services due increased capacity requirements.