I have used a mini home-datacenter to heat my house in winter (very effectively - I used a fan to direct the heat towards the intake for the AC system and ran the AC fan). But I decided against the HW heater version of it from a cost recovery perspective - we just don't use that much hot water and we had a then-new high efficiency gas hot water heater.

However, there's a fairly straightforward way to get halfway there: You can run a standard heat pump hot water heater and put the computers in the same room with it. The computers will heat the air, the heat pump hot water heater will cool the air. Won't be as efficient as a closed loop system directly connecting the computers to the HW heater but you also won't need to worry about whether the heat production and consumption are balanced.