They use both, heavily. An outage, like the one recently, severely affects them.

> In October 2026, George Barros of the Institute for the Study of War said the network had become "the backbone of military communications in Ukraine", used by land, naval and air forces, with both Starlink and Starshield (the US DOD service) used depending on the application.[60]

https://en.wikipedia.org/wiki/Starlink_in_the_Russo-Ukrainia...