In my view DS-5535 is for consular processing via embassy. If you are not Canadian citizen and need to stamp non-immigrant visa after immigrant visa stuck in AP via consulate, there is a chance you end up getting DS-5535 if flagged or on the CO discretion again. One guy was able to stamp L2 visa at border even though he was placed in AP(DS-5535) for EB category visa and was awaiting clearance by MTL. Folks are also getting green card via AOS in 3-6 months if they are in US on non-immigrant visas even though their cases for EB categories are still in AP for several months in MTL.