Nestor

Admittedly, I haven't dug really hard into this, but from what I can see, the Mimolite can read a voltage and return a value via Zwave. I mentioned thermocouples as they are generally cheaper than a Resistance Thermal Device. Something like the following http://www.farnell.com/datasheets/1734312.pdf will return a standard 4- 20 mA signal, which can be easily converted to a voltage with a precision resistor and read by the Mimiolite. Hope this makes sense so far.

Since you are considering the AEOTEC, which is Zwave, I suggest mating an industrial thermocouple temperature sensor to a Mimolite. Hot tub temps may be out of range of the devices you mentioned.