The only weakness I've identified in the OKW game play is if you are able to destroy one of their trucks. They will be unable to field a King Tiger but could still go for the 13CP Jagdtiger.
Heh.
This isn't even true.
If you build each truck once and lose them all you can still build the King Tiger. You only need to have built the truck in the past to "qualify" for the King Tiger.
Anyways, get some good sniper players in your clan. They're hell on earth to kill as OKW. M3A1 provides exceptional early game power. Tier 1 into Tier 2 into Call-ins is really strong against OKW.