Ben,
Black holes would still have the same event horizons since gravitational collapse forming the black hole happens in the IR, i.e., at very large length scales where G does not change at all. However, at extremely small distances, the effect of gravity would be weaker, hence singularity may not form in the center of a black hole. I expect that the macroscopic properties of a black hole remains the same, though. There has been some discussion on this subject, see e.g.,
http://arxiv.org/abs/1007.1317
Dark matter is irrelevant in this context, but from the supernova, CMB and LSS observations, we know that the cosmological data can be fit the \LambdaCDM model, i.e., cold dark matter, small cosmological constant, small amount of baryonic matter and radiation. So dark energy is probably the cosmological constant although the equation of state still is awaits for observational data. In the asymptotically safe gravity scenario, the cosmological constant would also run from its large UV value to the small IR value. However, note that the idea of asymptotic safety in gravity is based on the existence of a non-gaussian fixed point in the RG flow and it should be kept in mind that it not a trivial task to prove that.
Best,
Eray