The ET6 that came with my P55A-UD3P was on a CD-ROM that billed itself Version 1.0.2. The ET6 that came bundled with my P55M-UD2 was on a CD-ROM that billed itself Version 1.0. Uninstalling version 1.0.2 and installing 1.0 fixed the Smart Fan issue.

BTW - in theory the SPU fan header is supposed to report the RPM of the PSU fan to the MB. On my P55A-UD3P, it also powers a fan.