Interesting assertion, but the author provides little by way of corroboration.
According to Jayna Davis, Zaraqawi was in OK just prior to the bombing. From her website, referring to her book The Third Terrorist:
The notorious Dr. Ayman Al-Zawahiri, bin Laden’s No. 2 man, delivered the communiqué. Learn clandestine details about Zawahiri’s 1995 foray to Oklahoma to ensure the Murrah Building bomb would net the maximum body count.
I haven't read the book, but maybe someone who has a copy could check to see if and how that info is sourced.
See the post right above yours