So you really should talk to a plumber or energy expert, I don't think many people here have an idea how these things work.
You seem to though, the heat pump part will attempt to pull enough heat out of the basement to produce your hot water but it won't cause its cold here so the electric elements will do a bulk of the work. You will basically have an electric water heater, look at first hour recovery rates if concerned about capacity. Between you and me, stick with the gas fired chimney vented heater, gas always flows even when the power goes out.

I find it somewhat ironic that on my page the post right below this is Speed limits of 20 miles per hour have seemingly little impact on crashes, casualties and driver speed I didn't read it yet, just kinda funny.