To the best of my knowledge Thailand has a policy that no foreigners may fly a Thai registered a/c commercially. Every pilot that does has an individual exemption from the appropriate ministry. That said it seems to be a case of needs must when they can't supply local crew.
Policy - no. BKP, XO, and Kwaiyai's airline all have foreigners in both P1, P2 & P3 positions.
Air Asia were even operating internal services with Malaysan registered aircraft with Malaysian crews!!! Of course this was when Thaksin owned
Thai Air Asia!!!!