Sierra is supportive of it, as the site creator writes:
Quest Studios has always wanted to be known as a legitimate resource for commercial computer gaming music. Towards that end, I've contacted various game publishers to inquire on their stance for my posting their music on the Internet. Sierra On-Line, Inc. was not only pleased with the idea, they helped me by sending free games and music files so that I could establish a good sampling of their soundtracks.
Just found a soundtrack for the Conquests of Longbow there, and they are even using Ogg Vorbis (I'm personally amazed mp3 is still so often used around even on sites like GOG). The soundtrack is also available as MIDI.