From what I understand, Brian King (?) had the DDK legally.
I did some research on this. It's not so easy. Brian King got indeed some information on the P96 driver API, but there was never a formal contract. In particular, I would really hesitate to believe (based on that) that he had a license to sub-license or transfer the license to others. However, this is really required by the GPL. So that part of the UAE source does not seem to be under GPL.
In fact, if you check the file, it says "(c) Brian King" in the header, and it does not have the usual GPL clause on top. So it's really questionable in which state this file is, and whether you are allowed to derive any third party work from it.
Given that Picasso explicitly lists UAE as an option, that leads me to believe that UAE does not break the Picasso DDK license.
Possibly not, but is it GPL itself? It's at least questionable. For that, Brian King would have to have a transferable license on the DDK, but in fact - he got nothing, no formal contract, no license.
If I had to read between the lines, I'd say that if you make money off of it, they want their cut. UAE and other GPL drivers are not commercial so there is no cut for them to care about.
The trouble is now that: While I agree with your conclusion, that's nothing that is formalized in the GPL. You *can* make money from the GPL. T&A would have been much better if they would have put the DDK under CC-BY-NC, or something similar with a NC clause.
In the end, put it what you like, but the license situation is quite unsatisfactory with UAE, or any work derived from an API whose owners consider it proprietary. If you put that under GPL or LGPL, you're putting yourself under some risk - as you release it under (L)GPL and hence make some claims about its availability and possibility to use it in other projects. Promises that currently do not hold, or that at least are unclear, or at least unclear in some countries.
If you call that sloppy licensing from the original authors, I surely agree. But that doesn't mean that the story has to continue like this. What you're currently doing is again a sloppy/risky scheme by not knowing the details and backgrounds.
Again, if you want to be on firm grounds, "re-implementing" a closed source API does not help much. It only continues the trouble. As said, you have two options: Either try to get a valid license (and for (L)GPL, a *transferable* license) from the owners, or reimplement an rtg system with its own API.
So I don't quite see in how far your attempt can possibly clear up the situation. It cannot. It just adds more uncertainty on uncertainty.
