Yes, reselling or making them available in the sense of "here are the hex tiles for your use so you don't have to pay for them" would be problematic. Being open source doesn't change much, because even if they are not open source, depending on the framework or engine, you could often still gather them from the content files anyways. I guess you don't have to dump the tiles' source files in there?
Really hoping here that people are honest enough to pay for the work I've put in if they want to use them for themselves in their hobby or commercial projects. :)