TRACON Controller described a head on situation between two Tower controlled aircraft; complained to the supervisor who indicated visual separation was likely being applied; the reporter claiming supervisors are not doing their job.

Narrative

Runway XX [was] in use. A BE40 was completing an ILS approach to Runway YY and then continuing with an IFR flight plan to END with a Military BE90 departing Runway XX westbound. Tower asked Approach if they could send the BE40 on course on an approximate 060 heading; approach approved the request. Tower cleared the BE90 for take off Runway XX when the BE40 was on a 3 mile final to Runway YY. The BE40 went missed approach flying northeast bound over Runway YY with the BE90 climbing opposite direction underneath the BE40. Opposite direction traffic merged with approximately 300 FT between the two aircraft. I advised the FLM in the TRACON; observing that this was dangerous and needed to be brought to the Local Controller's attention. The FLM said that they were probably using visual separation and it probably didn't look that bad out the window. The tower airplanes were head on with one climbing under the other aircraft over the runway. This is not the only example of dangerous situations being brought to the FLM (all of them) attention and they just ignore the issues. If these problems are not corrected; there will be a major error or accident in the near future. Recommendation: The FLM's here need to have a more active role in identifying dangerous situations and correct the Controllers mistakes instead of trying to be their friends and looking the other way all the time.