I remember there being a Scizor lure set in 4th gen that ran enough defense evs to survive a bullet punch + stealth rock; now that Alakazam doesn't need to worry about the stealth rock damage this should be more effective.
Unfortunately, I am seeing that he still needs 216 defense evs to survive bullet punch. Am I doing something wrong?
Trying to survive Bullet Punch is what you're doing wrong, sadly. 216 Def EVs deducts far too many points from Zam's stellar SpA, using Substitute is a better way of going about this. As a bonus, it also prevents Scizor from Pursuiting or regaining momentum with U-Turn. On top of that, lure Zam needs HP Fire to make the 216 EVs worth it in the first place, which is an inferior choice given its other options.
Also, have people considered running Hidden Power Electric on the 4 attack LO set? Outspeeding Bulky Gyarados at +1 and OHKOing (110.3% - 129.7%) can be VERY handy and can probably net you an unexpected kill if you switch in Alakazam as they Dragon Dance. If you run Sash, then Stealth Rock is required for a OHKO.
It is viable for the reason you've stated, though I doubt it would become standard. One of those "if your team needs it" type of things.
HP Fire is a great choice. You don't have to rely on Focus Miss to take care of the large majority of things that will try their luck with Alakazam. Subs may curb the accuracy problem somewhat, but ultimately you're stuck using a shaky move against a majority of pokemon that would just die to HP Fire anyway.
This has been answered by myself and others already (no point cutting speed and coverage when you already screw these threats over with your other moves), but note that with a Sub, Zam gets 2 chances to land Focus Blast. That's a 91% chance, and if you land it on the first hit you still have an intact Sub.
Ah, and what do you run on a sash set? I was going to go Psychic/Focus Blast/Hidden Power Fire or Grass Knot/Shadow Ball!
Sash would run Psychic / Shadow Ball / Focus Blast / Filler, basically. The first three are pretty much non-negotiable on Alakazam, while the last move is up to you. HP Electric was mentioned previously for revenging BulkyDos, I'd imagine Grass Knot could work for Gastrodon or something, and you could even run Psyshock or HP Fire if you wanted.