What makes you think targeting would be an issue? The idea of kinetic orbital impactors is to not rely on an atmospheric glide for reentry, but to brute force straight through the atmosphere to maximize impact velocity and thus energy.

This means you speed up the impactor tremendously, e.g. with a rocket, and ram it straight down. The atmosphere is only 100km thick, and only the last 30km even have any meaningful density to offer noticable resistance. Yes, the impactor will create a massive plasma plume, but it won’t even have enough time to heat up itself, much less ablate or disintegrate before impacting the ground.

Targeting such a device would be extraordinarily simple with incredible accuracy.