Pass amps can they handle a highly reactive speaker load?

It depends on the Pass Labs model. Some of the Pass Labs Aleph models were unsuitable for such a load. Other Aleph models might be good. Most of the X series should be good.  I too am a fan of a lot of Nelson Pass's work, and it's a become a tad controversial to criticize his work around here lately, but I've found some of Stereophile's bench testing measurements a bit concerning. Despite general assumptions about the technical capabilities of these amps to the contrary; it appears as though more than a couple of Pass Labs products have struggled on the test bench when driven into some lower impedances. Could be a good or even excellent choice, but tread with some caution.

Ask Pass himself. Go to Pass labs and email him. Last I heard he still answers his own email. 

I'm building a First Watt F5 and I've been pouring over diagrams and forums on his amps as much as possible. Pass amps, in general, use simple circuits and as little feedback as possible. Some will drive a 2 ohm load rather faithfully. Others will fall flat on their face. Pass branded amps generally drive Focals nicely and their speakers tend to have some trying low points. Pass tries to get decent specs on his amps, but hell deal with a weaker damping factor, .01% distortion, or nonlinearity if it makes it sound better.