This has all already been covered quite well, but lemme throw my 2 cents in anyway!
MB tracks the actual CD, not the images on stores selling the CD (unlike digital where the two are harder to untangle). So if it doesn’t match the actual CD it’s a thumbs down. Amazon is very lazy with their artwork, but often enough it matches.
I personally wouln’t do this, I would just add the iTunes release and add the cover to that. If I wanted to store the image. With the ability to add a release group cover there’s no need to duplicate the ‘best’ image across to other releases.
However if others do it and the iTunes image matches the CD cover (the picture and the size etc) I do not vote ‘no’, as it still represents the release ok until there are scans. Scans are definitely the gold standard for physical.
We have a couple of spots for this:
Release group cover - this should (generally) be set to a nice clean, high res, square cover. People can choose that as their preferred source in Picard
Fanart.tv - If there’s no nice digital release to add to the group you can upload ‘fan images’ (e.g. edited/cropped etc) to fanart.tv. People can choose that as their preferred source in Picard
I would grab the biggest image from the iTunes server you could get, as it will be 1:1 to the one embedded in the tracks or whatever, just nice and big.
This is a good example of where I would add a new digital release to house a nice shiny digital release cover*. And then put the slipcase cover, even if worse quality, with the CD release.
Then we can have our pretty cover art cake and eat it too
*I was going to do it, but it seems to have been taken down from digital retailers apart from Spotify (which doesn’t have the best art). Seems like it was on iTunes, as well as Tidal, for sure, in the past.