It's important to remember that Orks are not stupid. That this is Imperial ignorance (heresy I know) and that Orks are in fact just as bright as dem humies. It even says just that in the current Ork codex.
They just think on a much more straight-forward cut out the middle-man practical manner, with no airs or pretentions or deceits and all those other things that them silly humans over-complicate their puny pink skin lives with.
What I'm saying is there's nothing wrong with a bucket as head protection. As long as it fits and da Boss can see it's a quick and pragmatic form of head protection. It would have to be a reinforced bucket (maybe some plates crudely nailed to it), with a suitable amount of Orky glyphs to show da Boyz that ee iz da Boss 'n' no messin' 'n' all, but that's just Orky common sense.