Leaving aside the "ethical grounds" issue (which strikes me as being very shaky, in terms of bringing actual ethics into DMing), the underlying issue (as I see it) isn't that contact poison only works when it touches skin; we all acknowledge that. It's that the issue of whether or not the character's skin is exposed apparently exists in a liminal state where there's reasonable assumptions for and against on the part of the player and the DM, respectively, and what to do when there's a conflict.
That said, I think there's also a separate debate to be had regarding the determinative nature of the dice, particularly where a particular aspect of the narrative sequence has no specified mechanical impact. It's not unreasonable, to my mind, to say that the roll in question operates in a manner that specifies the consequences of the scenario, with the specifics being made up after the fact to flesh out what the roll represents. In that regard, gloves should have a mechanical interface with that roll, ideally in the rules but given that's not the case, via house rules, preferably decided upon and agreed to by everyone ahead of time.