Even if you didn't want to track DKP for PUGs, just make people link their existing slot item. Sure, there may a person once in a while that links a trash BoE green, but that's why you check their armory if it seems suspicious.

Otherwise if you don't want to spend a lot of time managing it, Need before Greed and possibly let people moan and groan because they didn't get "their" drop. At least you know it's coming when they say "I hope my X drops". Sorry, maybe next time buddy! I don't control RNG

With dual-specs, and possibly switched specifically for what your raid needed, it's perfectly OK for them to roll on gear. That's why gear-homogenization is such a good thing for loot, more people rolling on gear, but a lot more gear usable by more specs.

The only thing I think isn't cool to need on is something that someone has put a lot of time into and is almost done, e.g. where they are only missing one BoP quest item ( legendary mace piece, darkmoon card, etc) that only drops from an dungeon/raid instance.