Doing some back of the napkin math, their contractual minimum of 2.5 kWh a day into your water heater works out to 75 kWh a month. This [1] site claims the average two person home uses 195 kWh a month, so it potentially could be a decent offset. I do wonder whether this quoted 2.5 kWh is energy coming off the server into your heater, or if it's measured somewhere else. Energy loss from thermal transfer would make a huge difference in measured input into your heating system.
[1] https://www.keysenergy.com/typical-electric-usage-of-various...