Thanks for the quick replies!
Indeed the intention was to convert to 20mm on the front and bolt-up on the rear, which as far as I know isn't possible on these hubs.
I think the freehub body is steel, I can't check now, but when I had the gear and spacers off (the freehub had fallen off of the hub on the way here), I didn't notice much indentation.
I've got an XC on the back of my Patriot, it's a great hub! I wouldn't have been annoyed had I not paid extra specifically to get the pro 2's, and wanted the conversion options!
Hopefully can come to an acceptable resolution with the seller, apart from the hubs the bike's in pretty good condition, but for every single bolt being hugely over-torqued!