Is it possible to use the Zee AM rear mech with a road cassette or is it strictly only the DH version that’ll work?

It ought to be fine- people have used mtb standard mechs and road cassettes for ages- but you probably get better chainwrap and a more tucked in mech body with the FR version.

It’s fine. No problems at all with mine and it’ll allow you to go to a big cassette if you switch bikes/go somewhere that needs a bit of climbing.

excellent. cheers.

I would suggest you tighten up the clutch spring if youre using it for DH.