I wish I could send out an email from that forum. 😅I'm pretty sure there could still be some copyright involvement if you were to blatantly copy the theme of another creator without their permission.
I created a topic on the ZetaBoards Support forum that is still there on Tapatalk now asking theme designers for permission to convert their work and a handful of people gave me permission to do so, which is the reason there are themes on my board that you used to see on ZetaBoards.