If someone had a necklace with a cross on it, can Amazon ban it? Should they ban it?
Yes, but not "Ban" but make "not visible". Things that cannot be banned are required religious symbols. Think Yarmulca or the Sikh turban (sorry I don't know the proper name). Where the religion requires wear. The cross can simply be worn under the shirt and not be visible. Dress code is all about visibility. You won't find a dress code that mandates undergarments for example. There is of course caveats with some jobs where wearing of the item presents an actual safety risk... Eg necklack falls out of the shirt and gets caught in machinery and now there's a bloody mess all over the floor. But even with protected items like a turban, if it displayed logos the company would probably be in the right to ask you to change into a different turban that was more neutral.
How about non-religious ear rings or other jewelry? How about a hair bun? Wedding ring?
Yes... I've worked in places that had such rules. A simple example would be the military. I've not seen Wedding ring restriction... but can think of several cases where that would be reasonable to also limit. Lots of people willingly stopped wearing their wedding bands in my motorpool after someone degloved a finger... I have seen plenty of places that ask people to remove other piercings/jewelry and it was a non-issue.
There’s generally some leeway given for cultural adornments. So the question is what specifically is bad about a BLM adornment?
If they're applying the policy fairly... which according to the court case findings they are/did... And that policy was effectively "no logos"... Then everything you've mentioned doesn't fall within the policy. I don't think I've ever seen a wedding ring with a Mountain Dew logo on it (like articles of clothing).
Here's a rendition of the general policy per a thread from 2 years ago https://www.reddit.com/r/wholefoods/comments/nxgnje/whats_the_dress_code/
You must wear plain tshirts (no pattern or multiple colors, only plaid) pants must be one color and in good shape (no holes) you can wear shorts in grocery and front end and produce but must wear pants in prep foods. Close toed shoes. Hats must only be whole foods logo and if u wear leggings you have to wear a shirt that is long to cover the butt. No pins on your apron and no logos or sports teams or bands.
Similar codes published by other users at https://www.indeed.com/cmp/Whole-Foods-Market/faq/what-is-the-dress-code?quid=1bk0o1sch5n8v93m in 2020. It's a quick google search to find more references if you'd like.
Nothing here would limit religious garb, rings or other jewelry, and I'm sure some other section would cover hair than the one that was furnished. Requiring a bun or other hair style for longer hair makes sense for anyone dealing with food, so at face value not illogical to see. So I'm not sure why you're bringing all this up. Could a company require compliance with these things? Sure... If you want to be paid to work, you follow the rules. Otherwise, go find another job elsewhere. It's like trying to work for a high end upscale restaurant... then being mad that you have to wear a suit.