Short answer: usually yes, but the rules are about rights, not about whether a machine helped you.

Redbubble doesn't ban AI art outright. Their IP policy asks that you own or have permission to use whatever you upload, and that it doesn't infringe someone else's copyright, trademark, or likeness. If you wrote the prompt and the output is yours to sell under the tool's terms, that generally clears the bar. Read the terms of whatever generator you use, though — a few of them claim rights to your outputs or restrict commercial use, and that's on you, not Redbubble.

What actually gets accounts nuked is uploading a shirt with a band logo, a movie quote, a sports team, or a celebrity's face in it. AI doesn't launder trademark. It just generates it faster.

Quality matters too. AI mangles text, hands, and fine linework, so zoom in before you upload. Redbubble's default wants roughly 4500x5400 px, so upscale anything that comes out small and check it at 100%.

For quick, clean starting points I've had good luck with https://shirtdesigngeneratorai.com — it's free, you type an idea, and you get a print-ready design without touching Illustrator. Good enough for a first upload, and you can iterate on the prompt until the layout works.

One last thing: don't dump 300 near-identical designs in a week. Redbubble treats that as spam, and so do buyers.