As far as I know it wont, if you want to buy the BAF & PMC DLC from Steam you need OA from Steam as well. However it might be different with Reinforcements.
Is it possible to even select Reinforcements in your Steam account?
Hey i have Arma 2 and OA (Steam) and reinforcements (Retail) And My Arma 2 dosent connect to my Reinforcements. When i play Arma 2 OA i have low textures for Takistan and the Factions. Does anyone have any solutions yet? I have put my Reinforcements in my steam folder and still nothing. thanks.