What would happen in a collision of an antimatter singularty and a matter singularity? Would energy be released if a black hole made out of antimatter and another of matter were to collide?
 A: No.
Courtesy of Star Trek, and numerous other Sci-Fi films and books, people tend to have the idea that anti-matter is somehow weird and mysterious. Anti-matter is just matter - it's anti only in the sense that a particle and anti-particle can react to produce two photons.
The stress-energy tensor that is the source of spacetime curvature makes no distinction between matter and anti-matter. In fact, as usually written, the stress-energy tensor contains energy density not mass density, where we convert mass to energy using the famous equation $E = mc^2$. So a black hole of mass $m$ made from matter and a black hole of mass $m$ made from anti-matter have exactly the same gravitational field.
So a merger of a matter black hole and an anti-matter black hole would be exactly the same as the merger of two matter black holes or indeed two anti-matter black holes.
Actually, to return to your original question, energy is indeed released when two black holes merge, regardless of what the black holes are made from. We expect merging black holes to produce copious amounts of gravitational radiation.
