It is obvious that you do not know what the GPL is about, and what its limits are.
The GPL is there to protect the programmers rights, they still "own" the code, it doesnt go into the public domain. People are free to learn from the code. Not companies, what kind of company would want to have a look at a game that old?
But you see, the actual license of the binary executables is not in question, the data files that accompany the executables are. The data files have not been released to the public, they are still under the original ROTT license, which means that you cannot distribute it.
You are right, the best use of any artists 'old' material is to have it as widespread as possible, but the artist still has rights on how the material is used.
They are pleased with the port, I posted about the port on the board and Joe3DR was impressed. That was before the binaries were released. However, I am sure that they would not be pleased that you would be obtaining a game that is still supported illegally.
Do what I said before, ask for a free copy on their forums. It is only then I will beleive you. Until that happens, you are just another fucking senseless bullshit vomiting moron that is going to get struck by a banhammer.