“Additionally, players can’t Need on a piece of loot if they’re wearing the exact piece at the exact item level” -Blizzard (https://www.wowhead.com/news/blizzard-clarifying-how-group-loot-will-work-in-dragonflight-and-no-weapon-boes-329108), although they changed to to exact piece at same or higher ilvl in between then and release.
Now I happen to know it worked for trinkets in pre-patch because It did not let me roll need on a heroic shadowed orb of torment when I had a mythic one equipped.
Transmog is a legit reason to roll need, as mogging an item does use the item.
Until you have the item in your bags in GL, it is not your item. Once you have the item in your bags, everyone else has the exact same options under either system. But before the item is in your bags, it is not yours.