Dual blade CwkPQ?

Dual Blades have separate skill IDs, so even though they're technically adventurers, they won't actually be able to activate the sigils unless they have the same Dark Sight that other thieves have AND sigils respond to DS, or Nexon actually adds the skill IDs for them. Considering Cygnus, Aran, and Evan skill IDs have not been added yet, Dual Blade probably won't either if their DS doesn't work now.

There is no good reason to exclude those classes (well, maybe Cygnus), so I think Nexon is being lazy about it.

Not a problem if you bring along a Thief mule. The fact that they can get in matters most to most people, since CWKPQ is all about obtaining MoNs anyway.