Believe he should drop 3 items every time. Last time we killed him on beta he only had his book (1 drop).
http://www.legacyofsteel.net/Archives/Post/2001-01-30
http://www.legacyofsteel.net/Archives/Post/2001-02-16
http://www.legacyofsteel.net/Archives/Post/2001-02-22
http://www.legacyofsteel.net/Archives/Post/2001-03-01
Think that's all the LoS posts about Velks. All show 3 loots.
Will search for more guild posts. But 3 drops should be very common if not guaranteed.
Nilbog - How many items can he currently drop?