How exactly would this work? The wearer/user would get the AC and unarmed damage of a monk 5 levels higher than the result of their hourly check via the "emulate class feature" usage of UMD?
It wouldn't.
Well, with UMD I'd think you're using...
Emulate a Class Feature: Sometimes you need to use a class feature to activate a magic item. In this case, your effective level in the emulated class equals your Use Magic Device check result minus 20. This skill does not let you actually use the class feature of another class. It just lets you activate items as if you had that class feature. If the class whose feature you are emulating has an alignment requirement, you must meet it, either honestly or by emulating an appropriate alignment with a separate Use Magic Device check (see above).
And potentially needing to get another DC30 to emulate a Lawful alignment if you're not already.
I think you'd need to manage a DC21 check to emulate a 1st-level monk. From then on, your monk's robe would be active, until you take it off.
So you're going to get 1d8 unarmed strike and a +1 monk bonus to AC.
UMD can't actually give you a higher monk level. You just emulate one for purposes of activating an item. That's only useful for items that require X levels of Y. In this case, no matter what DC you hit, you're not going to improve the robes.
Entertainingly, monk's robes work for non-monks. So no UMD check is required under any circumstances.
Any chance I could get a developer to weigh in on this? Though, Anguish's answer amkes sense if you take that tack that there's already a specific effect that applies if you're a non-monk to begin with.
Any chance I could get a developer to weigh in on this? Though, Anguish's answer amkes sense if you take that tack that there's already a specific effect that applies if you're a non-monk to begin with.
You can't emulate a class level. You can only emulate having a specific feature. So you could activate an item that required having a ki pool by rolling a DC 24 check (for 4th level monk), but you couldn't emulate having 4 levels of monk (because that's not a feature).