The two machines would not target each other if their paths crossed. Nomad was going after lifeforms and the DM was just out to blow up planets.
If some programming change induced them to fight, I think it would be a draw. The DM's thick neutronium hull would shrug off Nomad's energy bolts, and when Nomad got in front of the DM to try for a kill shot, the DM would be pretty fast on the draw and probably keep Nomad at bay.
Plus, it's not at all clear that an energy bolt worth "90 of our photon torpedoes" would pack the punch that the Constellation's 990-megaton explosion did. In "Balance of Terror," the Romulans' old nuclear warhead, the one they ejected with decoy debris, was vastly more powerful than a photon torpedo. It seemed like a lot more than 90 times more powerful.