Snooping around the internet before purchasing the game, I noticed that on the Xbox (I imagine the same holds for the PS3) the code needs to be redeemed via the Marketplace as can be seen in the following instruction leaflet:
When I launched the copy I recently bought through Steam, I saw a "multiplayer" key code pop up, but it apparently has nothing to do with the online pass (and the game didn't prompt me to enter a code at any point so far).
Your N7 armour in Reckoning is unlocked automatically with your online pass, available in all new copies of Reckoning, or by purchasing the Reckoning online pass on PSN, XBL . It unlocks with automatically with your PC registration code on Origin or Steam.
This possibly hints that there is no need for unlocking the online pass protected content on a new PC copy, but sadly the above is far from an explicit statement on the matter (all other mentions on the FAQ regarding the online pass are Xbox/PS3 centric).
So, how does one unlock the online pass content on the PC (specifically, with a Steam copy), if that is at all required? Also, if such unlocking is indeed implicit, what is my online pass bound to? My Steam account, perhaps?