I had seen that they said that since it's a 'tip' system and not directly in exchange for any services or the like then it'd be fine (and accordingly it's not something that can be charged back).

The dangerous thing would be if an artist were saying, "Pay me in X shinies for this art" and then they'd be like "You're using adult content with PayPal so we're terminating you"

...Think that's what happened with the people I've heard about?

Apparently some people, when paying for art, may actually even put graphic descriptions in the note field. (Which is one reason invoices are the safer bet because some customers are clueless AF).

Typical security measures like giving the PayPal only in notes, not publicly-facing or associating directly with art, are fine.