It would show bare skin/no items there, not the base item. For example, I have all of my crafters glamoured to something unique except for my GSM. I like my Ala Mhigan top for my GSM. Now, for this situation it's ok because all of my other glams are class specific so they just won't show on my GSM, but if I had something else - say, the ala mhigan gown - as the top for my Weaver, any time I'd switch to my GSM outfit I'd still be wearing it, even though I just want the base item I'm wearing. If you had the true griffin robe of healing on and you wanted that as your WHM outfit, glamming the yaefemi top of healing for your AST would mean it would also show on your WHM instead of the robe since they're not class specific.
Although of note, now you can just put the base item into the chest, apply it to the plate, then remove it and wear it.
