The canon “credentials” of the Illumians are chiefly manifest through references to the Greyhawk deities St. Cuthbert and Vecna (there are other mentions but they escape me at the moment). The “feel” of the Illumians is suitably “Grey” if one takes into account Greyhawk’s relationship with the Plane of Shadow; the largest single concentration of Illumians is located on the Plane of Shadow.
While there may be a natural, I think, reaction against Illumians in Greyhawk, IMO, that needs to be gotten beyond. The Illumians are not necessarily the outlandish gatecrashers they first appear to be. They are extremely secretive, even paranoid. And they can "turn off" their "headlights." They will thus not be found strolling through the streets of Greyhawk with their "lights" flashing. As they are "new," one might with some (retro-fitted) logic say that there may not be that many of them in the Flanaess for them to have gone unnoticed until "now." So, able to "blend," secretive and few in number, the Illumians become a DM option. "Canon" but hardly an explosive setting breaker, easily enough ignored if a DM doesn't care to use them.
The most intriguing aspect of the Illumians, however, is their possible connection with Mt. Mathmagahma (sp), which is located in the northwest Yatil Mountains and is described in the College of Wizardry (CW) product. CW introduces the concept of a primeval language that is magical in its very nature, with transformative properties. This idea has been further developed/revisited in Tome and Blood and the Complete Arcane. Of course, the Illumians are and guard the secret of the Word Made Flesh. The Word Made Flesh and the language primevel have obvious similarities. Whether they are actually related in more than surface way remains to be seen. I have not reread CW lately, so I am unable to speak with confidence. The possibility is, however, intriguing.
As, perhaps, the “signature” or at least most easily discernable feature of RoD, the Illumians should put no one off the product on their account alone. Buy RoD for the ideas, stick around for the Illumians. ;)
GVD
I like the Illumians, but I just can't see them as very "Greyhawky" (whatever that means). RACES OF DESTINY has lots of promise, and then seems to be lackluster in other areas (although I have not read the book cover to cover). Overall i will pass on RoD as part of a GH campaign proper.
Just my brief opinion.
.............................Omote
FPQ