It is unlikely that straight SST rules would work well for a WWII game.
Morale: while the flinch rules work well for SST they would need some modification for Stalingrad. Even the best troops fall short of MI, let alone bug, morale levels.
Weapon and personal stats: in SST there are relatively few weapon classes to deal with and personal stats are balanced to these classes. In WWII there was a huge variation in weaponry. When you consider that armor saves would probably go out the window, or at least changed, you have even less flexibility for modeling weapon effects. If designed to be compatible with SST most weapons would be in the single D6 damage die class. Now let's add in armored vehicles.
While I feel the core mechanics of SST would work well for a WWII/ modern game I do not think they should be directly compatible. If you want Bugs or other aliens in Stalingrad give them stats for that game.
