From what I could find:
Saiki Kanuma Ryu Kenjutsu is a swordfighting style which uses both the sword and sheath in it's combat techniques. This style which is used only by Shigure Takemi in the Rurouni Kenshin Movie - Ishinshishi no Requiem, is a quite versatile fighting style in which the practitioner can both defend and attack in an instant or fake out an opponent. When getting in the inital stance, the sheath is led out and tied to the left hand by the sageo (scabbard cord) while the sword is held in the right hand. One interesting note is that the saya (sheath) is covered with metal instead of being only wood, so that attacks can also be made with the saya.
I think there is another style that uses sword & scabbard together, but I don't know much about them.