Very interesting! I would have to suspect that Zahn's idea for the history of the Clone Wars was probably where Lucas first got the notion of Palpatine being the chessmaster behind them.

Lucas cribbing significant plot points of his movies/TV shows from EU material (after forcing the writers not to use them) isn't new. Back in the early 90s Rob MacGregor wrote an Indiana Jones novel (Peril at Delphi) whose first draft included as the story's narrator a 90-something Indiana Jones with an eyepatch and a cane. Lucas told him to cut out the bookends, claiming that "no one wants to see an old Indy."

Lo and behold, when the first season of The Young Indiana Jones Chronicles aired a couple years later, it featured a 90-something Indiana Jones, with an eyepatch and a cane, as the narrator in bookend segments in every episode. But the elderly Indy proved unpopular and was dropped from the show later on; in the current-day edits of the series he no longer appears at all.