There really is no point in doing so.
Just imagine when you can load an allies bunker/tunnel with your units...
Then imagine that you CAN'T see any commandset when you select such a structure. Then imagine that that'll mean that only your ally could be able to unload such structures and you would have a decent idea why it is not in...
If you want it enabled however, you would have yourself a huge job on your hand, mostly because it would require hardcoding a lot...and you can't with Generals...
Tunnel use
