THE EU was canon up until Filoni Clone Wars. It obviously had to be struck from canon when the lore between Clone Wars and the EU were at odds and Filoni regarded it as fanfiction. And if George was to ever make his sequels it would have been erased anyway. Even Zahn and KJA knew this in the 1990s.
George never really saw it as his Star Wars, but he was free to copy ideas and characters and places from it.