Is it possible to read out the "Album Artist" ID3 tag with spotlight query? I know that a spotlight query is capable of reading the "Artist" ID3 tag of mp3 files but is it also possible to read out (speak) the "Artist Album" ID3 field? This source doesnt say anything about it?
It isn't possible. You can check to see the metadata associated with a file by using the mdls command.

mdls ~/Music/iTunes/iTunes\ Media/Music/Artist/Album/Song.mp3


Try it with a song that has an Album Artist and you unfortunately won't see it in the output.