Specifically, fails to see evidence that dark matter is made up of Weakly Interactive Massive Particles (WIMPs) which should annihilate and produce gamma rays occasionally.

Dark matter dominates the mass (90% or more) of all galaxies, not just dim dwarf galaxies. The gravitational aspect of dark matter and is not widely disputed.

Ideally, this experiment would be run on a "dark galaxy" which contains only a dark matter halo and no stars, but we haven't found one yet. The issue with visible galaxies is there may be black holes and other sources of gamma rays created by normal matter.