Yeh it sort of implies that they know of terrorist groups in the Norman/OKC area, but maybe not all of them?
I would think one reason that Islamofascists would recruit people such as JH is that connections between the two would be very hard to find. One of the guiding principles of terrorists groups is the idea of cells. These cells are totally independent of one another and are not privy to the actions of each other. If JH ( who I believe fits the profile of someone who was ripe for recruiting) was approached it is most likley that only those who directly had contact with him would know of it.
I do not buy the lone suicide bit. Color me skeptical but the FBI does sometimes drop the ball.