It is entirely possible that Soulblighter has access to the same Binding Dream Myrdred had... we know he does something that has the very same, exact effect: we all remember how Cruniac 'broke the enchantment that bound a captured guard'.
It appears to be the Binding Dream at work their; if Myrdred used it during TFL to bind Legionairres, why wouldn't Soulblighter use it to bind guards for the Baron in addition to the normal thugs and hired losers?
Or perhaps it is a lesser spell. Brand new debate for ya ;D
-Welly