Yes, and installation is the same for stair runs as for level runs.
Cable Bullet tensioners can be used on level and sloped runs, and are always installed perpendicular to the post. The 7x7 braid cable we recommend is flexible enough to bend to a crisp angle as it exits the Bullet along an angled stair run.
When installing Cable Bullet tensioners, make sure the set screw channel used to tension the cable run is always angled away from the bend of the cable.