Unannounced wheel sucking is definitely a safety hazard and probably a traffic violation if done on a road. When I've caught people doing it to me on paths, I've told them I will stop suddenly for pedestrians and take no responsibility for signalling my stop or anything else to them. That has backed them off so far.

Pacelining of any kind on a MUP is generally unsafe. I do what I can to discourage drafting if I think there's any real likelihood of pedestrian traffic.