I'm only able to go by what R2R put in their .nfos, since I've not tried reverse engineering ilok plugins at all. But they claim that different companies use different ilok algorithms, and some of them haven't been cracked, yet.
Some seem to work a little like what you say, UVIs for example decrypt libraries against the ilok, and R2R has UVIEMU for that, but clearly it's not sufficient to crack all ilok plugins that way, or Softube's wouldn't remain uncracked.
And since ilok doesn't require a dongle anymore - there are machine and cloud licensing options too, and developers can opt in or out to each of the 3 license holder systems...