Anti-Matter Black Holes Assuming for a second that there were a pocket of anti matter somewhere sufficiently large to form all the type of object we can see forming from normal matter - then one of these objects would be a black hole.
Question is, would there be a difference between an anti matter black hole and a normal matter black hole - in terms of how would the matter/anti-matter make the black hole different, or would they be the same?
I would expect the answer to be that the black hole formed from anti matter would retain the anti-matter properties in such a way that if it was to merge with a black hole at same size formed from normal matter that they would annihilate  each other con convert into pure energy - Would that be a correct understanding?
 A: No, the merger of a matter-formed blackhole with an antimatter-formed blackhole would not cause the blackholes to be converted into energy -- putting aside the mutual annihilation of accreting matter/anti-matter outside the event horizon, which certainly would cause a lot of fireworks. 
Event horizons are like Vegas, what happens there stays unknown to the outside world. The energy of matter/antimatter collisions cannot escape the horizon. Remember that the event horizon isn't a physical surface, like an egg shell, it's just a "point of no return." As two black holes "merge" they just have overlapping regions. If, an antimatter particle originating from one region happens to meet its complement inside another, it's no different than if you had such a collision by happenstance inside a single blackhole; if you had an entire antimatter-formed black hole's worth of particles that would certainly make for a large number of such annihilations, but the conversion of mass to energy inside the event horizon would be unknowable to an external observer. 
A: Since a black hole is essentially an expression of a sufficiently deep curvature of space-time in general relativity, and gravity from anti-matter is expected to be the same as the gravity from matter, I would say there is no difference.
As a practical matter, I would expect that it would be very unlikely that absolutely all the anti-matter would get sucked into the black hole. All instances that have been investigated involve the formation of relativistic jets of matter expelled from the poles of the accretion disk. These jets would give themselves away as antimatter when they ran into normal matter and the high energy photons (gamma rays) characteristic of matter-antimatter annihilation would be emitted.
A: According to Thorne (Black Holes and Time Warps) all matter that approaches the black hole singularity is reduced to a common degenerate form - matter and anti-matter alike. The way I interpret it, matter ceases to retain any resemblance to what existed outside the black hole. The attributes that distinguish matter and anti-matter are stripped away. 
According to astronomer's newest observations and the belief that black holes may play a fundamental role in the evolution of galaxies I wonder now if this may be leading towards an explanation of the broken symmetry after the big bang. Perhaps black holes could explain where all this antimatter has been trapped - hidden behind the horizon. Is that possible, and if so how and why?
A: That other question mentioned in the question-comments also discussed annihilation of particles and neutralization of electric charge inside the event horizon. In either question, the no-hair theorem trumps all. If GR is the end of the story, particle identity is destroyed by the singularity. Even if post-GR theories of gravity rescue the Universe from the creation of singularities, it doesn't matter because the form of the mass-energy inside the event horizon doesn't matter to the outside world.
A: To put it simply, 1 black hole + 1 antimatter black hole of the EXACT same size would result in the release of more energy than anyone on earth could possibly comprehend. If matter + antimatter = annihilation, then doing it on a large scale would just mean releasing more energy.
To put it even more simply, being a "black hole" simply means it's achieved enough mass to collapse at an atomic scale under its own gravity. It's still made up of whatever went into it.
In conclusion, 1 particle of matter + 1 particle of antimatter (times however many particles you used) = 2 gamma rays (times # of starting particles)
