If we assume that a black hole does form then they do reach Planckian distances when they collapse towards the singularity. The two electrons are attracted to each other my gravity so they will not remain 2km apart. So we can only say that the UV effects can be ignored if they are hidden behind the horizon. But the existence of the horizon really depends on the whole dynamical history of the electrons. So we can't really assume that a black hole does form. So I would say that the idea that we can ignore the UV is actually circular logic.