My reading of the text in the LIAB 37 page doesn't necessarily support (or specifically deny) the Parson=Hippiemancer idea. The only line I was able to find that seemed to allude to this was...
Marie would know. At the roots of it, this was her plan. "What Hippiemancy neeeeds, Jonnis my true friend, is da one thin it con't evah have. A warlord. A souljah!"
It must have taken thirty turns before Marie had wrapped Janis' head around the idea of a warlord who would fight against war itself, and another twenty before she could imagine one who might be good enough to win.
My interpretation, honestly, is that the Predictamancer/Hippiemancer side of the Caster Conspiracy Clusterf%*& intended for the Perfect Warlord to be someone willing and able to end war on Erf. The Hippiemancers under Janis want a warless Erfworld as an endgame goal; Parson is a fairly unique confluence of traits that make this potentially possible.
Parson is skilled enough to be a dangerous force, clever enough to truly break Erfworld's rules and achieve their goals, and most importantly compassionate
enough not to abuse it. A weaker, lesser man could fall into some brutal temptation. An outright evil person with Parson's talents could... well, could produce a really, really bad thing. (Consider someone entirely willing, as Parson is not, to Order units around out of sheer spite, vanity, etc, in control of enough of Erfworld to, for example, "end war" by causing a permanent stalemate between his own side and the entire rest of Erfworld? Scary)
I still really doubt that Parson is a Hippiemancer and believe Janis was blatantly lying, but I suppose the possibility still exists. I'm more apt to believe that Parson not autofragging on the portal was a result of him being an anomaly in Erfworld.