That's what the card says anyway.
Played through as Diana, tested all NPC side missions, all fights leading to the three alien endings, and everything worked fine.
Achievements unlocked as they should, except for Knighting, Solidarity and Thank You, which for some reason were already unlocked in game and had to be synced to unlock in Steam. I should have already unlocked far more achievements than those if it used the old game files, and they shouldn't have been there if the Steam copy started over (before syncing). In any case, it probably wouldn't have happened if I hadn't played the game already, so no big deal.