Dude the link I referred you to is on the official site.
Lucasfilm has a canon they follow. If what was written in that Labyrinth of Evil novel goes against what George Lucas had planned for ROTS, it would have been changed.
As it is, since it was a more recent novel, my guess is that it in no way interferes with Episode 3... and whatever it says about Sifo Dyas is the truth.
Same thing happened when Timothy Zahn wanted to make Joruus C'Baoth an insane clone of Obi-Wan Kenobi in the Heir to the Empire books... George Lucas wasn't cool with that, so they changed the character.
