While Marc Stein was the first to confirm Sacramento's interest in Jack, Jason Lloyd of the Akron Beacon Journal has provided some more specifics:

Jack has played for Michael Malone in both Golden State and New Orleans, two of his best years in the league (although it should be noted Malone was an assistant in both those spots).  Jack is 30 though, and has two more guaranteed years past this one (his final year is just $500,000 guaranteed).

In my personal opinion, if these reports are true, I don't think Thornton or Thompson alone make sense for Cleveland.  Trading for Jason Terry makes more sense than either of those guys since Terry offers Cleveland substantially more savings and another experienced veteran.  It will probably take a little more tweaking than just Thornton/Thompson for Jack to make a trade work.