From what I remember from Lamannia during a dev Q&A session, vorpal strikes should allow you to use your dex as your to-hit/damage if you take the first two core abilities from the ninja spy tree. I know there is a thread identifying that it is not working with "sting of the ninja" but should it be working with the core abilities as well?
at the moment the #1 enhancement doesn't work the way it says it should. (#2 works. or so it claim)
i was using the scorching wraps(from 3bc) and the to hit didn't use my dex bonus.
the way it should work,like with a sword:
http://imageshack.us/a/img835/1497/gajk.jpg
the way it does work at the moment:
http://imageshack.us/a/img692/6316/0el7.jpg
i sent them a bug report. let's hope they work it out.
edit: seems that the dex to damage works(wraps get dex for damage like the sunblade) the to hit bonus for dex is not working yet.
as my dex is +6 and my str is +1. which lead to the sunbalde +15 over the wraps +10.