Interesting claims, alas unsubstantiated. Let's quote the readme of picasso96.lha uploaded by Tobias Abt himself for some facts:
"Picasso96 is ShareWare. Requested fee US$20 or DM30, free to use for PicassoIV and Pixel64 users (the manufacturers of those cards already paid for these licences) and the really few ones that already have sent us a donation."
Clearly Picasso96 is shareware for users. I don't see anything about any fees for people who write additional drivers. And why should I not be allowed to write any software of my own and publish it? I'm also allowed to build LEGO bricks compatible with the original LEGO bricks and sell them (there is a long history of LEGO case law). If I want to have my driver included with the original package, yes, that's something for which the authors could demand a license fee.
Making a card compatible to the two cards mentioned in the readme and exploiting the licenses that were paid for the two original cards seems to be an anticompetitive action but I'm pretty sure the original license hold won't mind. And if the picasso right owners don't mind, who would?