Both Beck and Cowan report that Wilber misinterprets Spiral Dynamics. However, that might be caused by their over-attachment to their theory (Authors are biased to defend their theories), so they want it to be central and not subordinate to Integral Theory.
This point is made in one of the answers to What We Are, That We See. Part I: Response to Some Recent Criticism in a Wild West Fashion in Part II: What Is the Real Meaning of This? (While the response does not mention Spiral Dynamics explicitly, I’m pretty sure it includes it):
the thing with lots of Wilber critics is that they have their own valuable (shadow?) baby that they don't like to have inserted into a bigger picture, a mosaic, such that their baby (their "part") is no longer front and center and the most important baby. rather it becomes (with integral eyes) a part of a larger picture with other equal babies, and they HATE that.
when you have this attitude about your "baby", it's too easy to call someone else's unattached attitude (integral) to your baby as skimming. 2nd tier is all about creating a bigger picture for its own sake, it's all about fitting as many perspectives as possible into your line of sight. it is almost by definition a view that describes the world from a 50,000 foot level. what other single perspective can include as many truths as possible?