U90 Controller described an unsafe event when a flight of two military jets failed to turn as directed during opposite runway operations.

Narrative

I was working an Air Force recovery to DMA; at night the Air Force departs Runway 12 and recovers on Runway 30. Generally this is not done at the same time; but this night I had Aircraft Y inbound for a ILS to Runway 30 and I requested it with DMA as Runway 12 was the active. They approved it and then asked of they could release a IFR flight of military aircraft off of Runway 12. I said approved heading 300. As Aircraft Y approached the localizer DMA called to advise that Aircraft X was rolling and per their 'regs.' Aircraft Y could not be on final prior to Aircraft X being on frequency; so to not bust my MVA's as soon as Aircraft X did there rolling check on my frequency; I turned Aircraft Y to final and issued traffic departing to Aircraft Y. Aircraft X checked on frequency climbing out of 3;000 MSL with the transponder off. At this point the two flights were head on with Aircraft X flying heading 120 and Aircraft Y heading 300 with 4 NM apart. I instructed Aircraft X to turn left heading 300 as DMA had assigned. The aircraft replied that they would turn left in 5 seconds. I then issued the traffic and adamantly assigned the turn again. Once Aircraft X finally began the turn I shipped Aircraft Y to tower. Recommendation; have something in place that requires the pilot to turn to the assigned heading on departure or require more separation between opposite direction approaches.