Hi Shawn
On a number of Eurocopter aircraft, the series actuators are down stream of the 1st stage hydraulic boost (autopilot hydraulics) so that they are working against a hydraulic lock unless the pilot moves the stick. On these aircraft, SAS works with or without force trim turned on, with or without the pilot holding on to the cyclic (though not holding on to it in SAS mode is not a good idea for too long!). With autopilot hydraulics turned off, there is considerable resisitive force built into the unpressurised hydraulic pack - again the SAS actuators will move the head servos rather than feed back into the cyclic even if the pilot is not holding the cyclic.
As others have said, SAS is all about the system generating control inputs to resist rates of pitch, roll and yaw. Whether the input data is from rate gyros, FOG/laser gyros or differentiated attitude/heading doesn't really matter.
ATT is about the system generating control inputs to maintain a particular pitch and roll attitude, so that when the pilot releases the controls, the pitch and roll attitude revert to the memorised datums. Typically those datums can be adjusted to new values using the cyclic coolie hat and/or by temporarily releasing the stick trim (system sets the datums to the values current at the moment the trim is reengaged)
HC