As far as I am aware, there is no legal basis for anyone to demand a say in what you do with your renders, so long as you observe their copyright (i.e. the original product cannot be extracted) and trademarks. The so-called "licence agreements" that people talk about in readmes are not legal documents. Click-through licenses of the sort you see for commercial software MAY be legal. I find the "I don't make money out of this freebie so why should you" attitude to be near incomprehensible dog-in-the-mangerism, but it pays to keep sweet with people who contribute free stuff to the community. So it is polite to respect their wishes. But a vendor who thinks this way is clearly in the wrong line of business.