I would make sure there is isolation from other outlets to prevent a lightning event cascading to other outlets in the UPS or surge arrester. I would keep a separate UPS for the cable modem if you can afford it. HFC Coax by code should be grounded at the building point of entry to inhibit some surges. Lighting has a lot of energy and it can behave unpredictability. I would not call anything is lighting proof. I have seen it jump through copper network cables, switches, fiber that had a location messenger, and even up a wall through metallic wall paper.