tasuku has a huge list of artists that he composes/arranges for.. as for music like tasking / taskinst / the rest of the task-interludes.. I don't know if he does those for other artists.
http://tbp.tearbridge.com/?p=artistinfo&id=tasuku
Here's a list of his arrangements and compositions since 2001. (作曲 is composition, 編曲 is arrangement)
I don't think he worked on the song "Beyond Hope" though. It was done by a group from Korea called S.F.A for a game. It's possible that they used a similar sample of some violin sound byte seeing as how Beyond Hope changes into a completely different song after the intro..