The Guandao is a bladed pole-staff weighted for martial combat. My idea would be that it scales off of both Martial Arts and Long Blades.
So, if you had Competent Long-Blade skills, but only Bad Martial Arts skill, the weapon would scale off of the Bad skill scoring. The trade-off for the ridiculous scaling would be that the weapon has a much higher to-hit ratio and damage.
Of course, I would assume this weapon would be pretty expensive, probably more expensive than the katana.
For more information; https://en.wikipedia.org/wiki/Guandao