I'll preface this reply by saying that I'm not a Denshield guy. With that out of the way...

"The seams halfway down didn't line up great, so he used fiberglass tape & a sealant, then drywall compound to smooth over. " It might just be terminology, but the "fiberglass tape and sealant" are fine, but instead of "drywall compound" he should have used thinset. Now if the "drywall compound" that he used was setting mud, a powdered compound that he mixed water with, that it okay. If he used the premixed drywall compound that comes in a resealable plastic bucket, that would be a poor choice, as it is water soluble.

As to his solution? I'd rather he use expanded metal lathe than chicken wire. But that's a personal preference. I think lathe holds mud better and resists rust better than chicken wire. But again, that's a personal preference.

If he fastens the lathe with the hot-dipped galvanized nails going through the Denshield and into the wall studs, then you're not violating the "no mechanical attachments" exception that GP specifies with Denshield. The lathe will be attached to the studs, not to the Denshield. Overlap lathe joints by a couple of inches and wrap the lathe through the corners instead of having two pieces of lathe meet in the corners.

All of the waterproofing should be done to the face of the Denshield prior to the paper and lathe going up. So have the seams properly detailed, etc, before applying the lathe and mud.

Now, I'll express one concern. Maybe not "one" concern but perhaps "another" concern:

Lightweight (Denshield-type) shower construction is pretty easy. Floating shower walls with mud generally isn't. I'd be worried about someone who completely buggered up a Denshield installation being able to pull off floated mud walls in a shower surround. At least find out if he's floated mud walls before. Maybe he simply had a bad day with the Denshield.