How much would it take to solve the missing antimatter problem? Is there enough? Is it testable ever?

I don't think it would answer the question. Even if half the dark matter was dark-antimatter because the problem isn't just "why isn't (*) there as much matter as matter, but "why aren't there as many anti-electrons as electrons, as many anti-protons as protons, etc." If these particles were formed from the initial conditions of the universe, then you would expect them to be formed in matter-antimatter pairs.

 

(*) The question is, I think, more accurately, "why wasn't there an equal amount of antimatter" because if there had been, then it would have all annihilated and we would live in a universe made almost entirely of photons. Or rather, we wouldn't.

The missing antimatter is normal matter, so as Strange suspected it would have no effect.

If dark matter collided with dark anti matter, the result would be the production of photons. One would expect these photons to be visible, unless they were some form of dark energy. Would a dark photon then be a photon that did not interact with normal matter?

There are a number of experiments attempting to detect the radiation from the annihilation of dark matter-antimatter; for example: http://www.space.com/17133-dark-matter-annihilation-gamma-rays.html

If dark matter collided with dark anti matter, the result would be the production of photons.

 

Would it? Photons imply an electromagnetic interaction.