Enough collector area for domestic HW and hot tub + heat exchanger questions

As if you didn't already have enough on your "plate."
http://www.toad.net/~jsmeenen/recovery.html
Here are other ideas to mull over.
http://climatewell.com

Elbie, does the hot tub have a heat exchanger or does it heat the water in the tub directly? If it is indeed a heat exchanger then your idea will work. If it does not have a heat exchanger then you may have to rethink.
 You said you are in a freezing zone so I would think that you would use an antifreeze loop. If the tub has a heat exchanger, then do as you said. Send the heated antifreeze into the domestic hot water heat exchanger tank and then send the return water into the hot tub, then back to the panels. Install bypass valves for those times you do not wish to heat one or the other.
 If the tub does not have a heat exchanger then you may have to draw the water directly from the tub to be heated. It should have a drain somewhere. Pump the water from the drain into the panels and back into the tub using a hose so you have an air gap to prevent syphoning. Modifying components may void warranties.
 Using this scenario, you could skip the domestic hot water and only purchase the panels, pump and piping.
 If you do not use the tub year round, add a tank, flush out the piping and panels and switch over to solar hot water the rest of the year.