It's not that reactors are needed in the permadark regions, it's just they they tend to be very cold and it should be easier to dissipate heat from the reactor.
I thought that it's hard to radiate-away heat in vacuum?
Dump the heat into the ground.
I think there is reason on mars - there is a fairly significant source of water there (ice). I guess this wouldn’t explain the moon though.
The darker locations are co-located with the largest water ice deposits which are exciting for the possibility of a human presence.