So StarFleet aren't willing to do a favour for a major power who (who knows when the wormhole might reappear) they were previously at war with and might be handy future allies?
I didn't think the reasoning made much sense when I read it and I don't think it makes much sense now between a contrivance to get Odo back to the AQ - there were a hundred other ways of doing that and keeping him there that make more sense...
Apparently not, as Starfleet has its hands full with the Typhon Pact. And, as the Dominion had closed its borders to any vessels- including Federation ships- it's not likely that anyone approaching their space would be well-received, regardless of whom they were transporting.
Odo is one of the Dominion "Gods", I'm sure that he has the power to grant a Federation ship taking him home passage through Dominion space.