As previously stated, Chad Hansen ("A Tao of Tao in Chuang-Tzu"; Experimental Essays on Chuang-tzu) makes a great deal of what he understands to be Shenzi's (Shen Dao) "absolute mysticism" as a means of contrast with Zhuangzi's abandonment of all "absolutism". In other words, he understands Shenzi to have asserted the existence of a metaphysical Dao, the context of which informs our life-engagement, whereas Zhuangzi made no such assertion, but was completely skeptical of any such metaphysics, and instead suggested there are as many daos as there are people to hold/walk them. If his reading of Shenzi is correct, then I agree whole-heartedly with this conclusion. However, I am not so sure that this interpretation of Shenzi is entirely correct, or if it is true that he believed in a metaphysical Dao, that that should be understood as forming the foundation for his philosophy generally. In any case, I have long found the presentation of Shenzi's so-called 'proto-Daoism' (and 'proto-Legalism') in the Tianxia (33rd) chapter of the Zhuangzi quite thought-provoking, and Hansen's use of him has renewed that interest.
A few biographical facts about Shenzi are in order, but first it seems important to say that what makes his thought particularly interesting to me is that it is a philosophy of life. He asks and answers the question, how best to live. This is the norm for classical Chinese philosophy, but is frequently not the case today where philosophical inquiry seems to exist for its own sake, as a self-fulfilling intellectual exercise (Knowledge for knowledge's sake). Thus, we might discuss Shenzi in a 'scholarly' manner without reference to how it informs our living, but this is not what this inquiry is about. My interest is in whether he has something to add to or can shed further light upon that way of being in the world advocated by Zhuangzi. And it is this way I am endeavoring to better understand for the purpose of growing and living my own philosophy of life.
Shenzi (ca. 395-315 B.C.E.) is thought to have been a contributing scholar at the Jixia Academy in Qi, where philosophers of many stripes were invited to reside with the financial support of the government. His dates make him as an elder contemporary of Zhuangzi (ca. 369-286 B.C.E.) and thus his thought may very well have informed that of Zhuangzi, though they make no mention of each other.
Shenzi is considered both a precursor of both Daoism and Legalism. The latter believed human nature to be essentially 'evil' and thus necessitating the constraints of law (fa) with its rewards and punishments. What makes Shenzi a possible influence upon both these otherwise polar opposite points of view is his belief that nature is amoral. This was a break from Confucianism which understood 'Heaven' as a moral force which, if we could understand its principles, would guide us to the only best way to live. Mencius, possibly another member of the Jixia Academy, was the greatest advocate of this view, and consequentially declared human nature 'good'.
From here, we will take yet another look at Shenzi from the perspective of the Tianxia.
You can check out Scott's writings on Zhuangzi here.