We asked another 343 employee at RTX about this, and they said the exact opposite: 343 does not endorse the use of any modded content and using any modded content, including putting it on your fileshare or even playing it on XBL, would be grounds for banning. The only possible acceptable way to use modded content, we were told, is if you do it 100% offline.

This was someone pretty high-up in the studio, so it sounds like they don't have a cohesive message on this. I'm not even sure the folks at 343 would be making these decisions about banning, anyway, since it's all tied up in the XBL TOS. It's probably another division entirely that does the bannings.