The air fan on my PC has a bigger motor than that! You wouldn't need much to get a small current going, but anything bigger than a tiny impeller/prop will burn that sucker out.
I disagree entirely. That gearmotor will have way more torque than any standard PC fan motor. it's geared down. That's why they call it a gear motor. I see absolutely no reason why it would not work. Much would depend on the size of the propeller, but I don't think it would have to be a huge one to get the job done. In any case, the $6.65 price tag makes the risk rather trivial. I'd give it a try.
It is not only the consistent HLT temp, it is also having a decent cross flow on the HLT coil that eliminates the thermal barrier. The coil will have the exact same temp as the water in the HLT. Without stirring that is not possible.