Hmm, maybe? The effect of that licence seems to be to prevent the person building on the game from selling it exclusively - since anyone who buys it is then entitled to distribute it for free.
I guess it's ok on the grounds that (a) people share RPG PDFs all the time anyway, and people can generally be trusted to pay for them; and (b) if anyone finds it off-putting they can always choose not to use this particular seed.
I had understood that they could separate any of their own product-identity as long as they redistributed any directly copied content under the same terms, but if there is any confusion I'm totally happy to use cc BY or even CC0 instead.
