Fan PWM Emulation with SATA power
I ended up doing some testing on an old computer with a 4-pin fan. First I tested the ground pin and there was continuity with all the ATX COM pins. Feeling confident, I popped the ground pin out of the 4-pin connector and it fit nicely into a SATA power connector on the ground pins. After powering the computer on, the fan worked nicely.

So, as far as changing fan ground to SATA ground, the are no worries there.

Thinking about this answer though, I realized that I never tested SATA power through the fan PWM. I suppose that I should check out that Intel spec to make sure I'm not pushing to much amperage to the fan PWM.