mounting un-vented range hood in plaster and wood lath wall
I'd be inclined to overengineer this; you can imagine that having a (greasy) range hood come down over a source of heat and/or flame would be bad.

What if you drill-and-cut new keyhole slots to match where your studs are? I think you should be able to fit two of them in a range hood.

Note that this is probably only an acceptable solution if the studs are reasonably centered on the range hood.