Pretty much all the RCDs sold here now respond to pulsating DC as well as AC imbalance.
I'm going off at a tangent slightly here, but I understand that back in the 1960s there were concerns with some of our utilities over the distortion that was being introduced into the local LV distribution networks. It was put down to the fact that at that time there were huge numbers of radios and TVs of the AC/DC live-chassis type, which just used a simple half-wave rectifier in their supply. It resulted in the positive half-cycles being much more heavily loaded than the negative.
