An archive of disturbing illustration
There was a disclaimer at the beginning stating these were parody, with strip clearly labelled as being not under the approval of United Media. Nobody could ever assume these were officially sanctioned representations of Dilbert.
Part II. Conclusion
Fair use of copyright includes the right of parody. This right is not negated because the person being parodied does not approve of the end work. That's the whole point behind the idea of parody itself, and the reason that fair use exists. Otherwise, parody could never exist.
Nonetheless, the parodies have been removed, there being other battles to fight.