Here is a quote from Kriss3d, a Super Moderator here on d2jsp: "Its virtually impossible to tell with 100% if a item is duped or not.. you cant tell.. if you could.. ppl wouldnt be trading duped items.."
-- I posted in general help a question asking how to tell if an item is legit or not. A level 90 monster could have very well dropped these gloves. There is no possible way to tell if they are legit or not. However I can tell you that I have had these gloves for over a year now and they have not poofed.