The flaw in both theories is SnapOn was making plain 5/8 drive sockets in the 20's , so there were sockets available if someone wanted to mate them with an impact gun and demonstrate the socket-schrapnel-effect....
Souix was a contractor to the gov, so it's possible the 5/8 drive impact sockets were just to fit those 5/8 guns, only speculation tho....
I'm not sure the gov was as worried about field personnel stealing tools as the tool companies were worried about getting gov spec'd tools turned in for warranty service (stealing uncle sam's tools gets you an all expenses paid holiday in leavenworth).
Then again, the black market was a booming business, so who knows...