True, but even though you redeemed Delta miles, and your US-bound flight is on DL, the flight that will dictate the bag fees and the placement of priority tags will be an AF/OS codeshare flight, so that's why I think AF or OS forum is best.
Edit: Actually, I looked up the OS site for baggage rules on their aircraft:
link
If you combine an Austrian Airlines flight with those of another carrier, please note that this airline's rules will also apply on Austrian flights if operating the longest or most significant part of the journey.
So you may be able to get 3 bags. However, can't really say much about the priority tags since OS doesn't have "Sky Priority/Skyteam Priority" tags