I think military dishes aren't necessarily pointed at friendly satellites. They might be eavesdropping on foreign satellites and the domes might serve to conceal which from prying eyes. I suspect large dishes may have utility in such a role, since they might be listening to low power side-band emissions from those satellites (e.g. Van Eck phreaking.)
Either way though, I don't think radomes are meant to conceal the position of the satellites themselves.
