I doubt that HBGary had the source to Stuxnet. Even the source is not that useful. Its infection vectors are known. It does not really use novel worm techniques. They would not be able to sign a different rootkit payload without the stolen certs. The source does not give you control of the command and control infrastructure, so they cannot use or update any of the currently infected machines (this is speculation, I do not know the specifics of Stuxnet in this regard). The PLC payload is useless and would have to be rewritten and tested for a different target. Basically, having a copy of Stuxnet and/or the source for it is useless for using it as a weapon.

The source would be great for the people looking for evidence of who wrote it and what their intentions were, but that is about it.