I have never heard of the possibility to hack something like this. All I know of is cheesy sync-error tactics that apparently some people use.
that's true, it is not (or should not) be possible to hack ressources or spawn in new units, as this would result in an immediate sync error and the match crashing. which would then count as drophacking of course.
I have 6500 hours in coh2 and I never saw ressource or unit hack. And I'm sure nobody else saw it either