I understand that a single WIMP interacts weakly with individual baryons, or probably even planets, but black holes should be able to slingshot the individual WIMPs they encounter. According to the Virial theorem, this transfers impulse largely to the much lighter WIMPs? So do they contribute to heating the CDM in a galaxy/cluster? Does the CDM this way contribute to the early inspiral of black holes?
The answer is currently nobody knows. It seems that, as black hole (or any other compact objects) inspiral, they may heat the dark matter halo (Figure 3 here). This is due to the gravitational slingshot effect.
It is worth noting that there is no consensus about the amount of merger events in history, however, so deriving anything very robust on their effects on dark matter is a bit dubious. This lack of consensus is due to 1) lack of constraining observations 2) lack of numerical accuracy to resolve cosmological scale simulations on the scale of black holes