Does ArduCopter do RC input smoothing?

I see that Betaflight does its own smoothing of the RC inputs (4.3 Tuning Notes · betaflight/betaflight Wiki · GitHub) and therefore recommends that the pilot turn off ADC filtering on the TX.

Does ArduCopter do anything like this or are RC signals immediately acted upon?

Yes. It used to be called RCFeel, and out still is I the Tuning section (for applying to a transmitter tunning knob and channel) and in the fill parameter list it’s called ATC_INPUT_TC ( From memory) and the default is 0.15 but use 0.2 or there abouts for softer input