By accident I discovered something that might work, though I haven't had a chance to test it.I was base NOd soldier attacking at the opening of the GDI base. I took out a few ground troops and the way was clear--then the GDI harvester rolls past me and a light bulb comes on over my head. So I get in line behind the Harvester and as I round into view of the AGT it starts pummelling away at me, but the harvester is in the way so I'm sitting pretty using the harvest for cover. Of course, then a GDI infantry came and blasted me to hell, but....
What if you did this with a cloaked Black Hand. I know GDI troops can see u if their in range, but I got within about 2 harvester lengths of the AGT with a normal Nod soldier before someone saw me. The cloaking might give you the concealment to sneak behind the harvester without GDI troops seeing you. I haven't had a chance to try it though. Think it would work?