Does incoming AC affect jitter?

My guess is yes; but can’t find much online about this. Another way to put it is: would a regenerator reduce jitter?

It can, tho a little indirectly.
Jitter is caused by not knowing exactly when a signal goes high or low. That decision is often based on comparing voltages like when did it cross the middle voltage between the power supply and ground. If the ground or power is fluctuating then this decision comes a little early or late, i.e. jitter. So insofar as a regenerator helps in cleaning up the power supply or ground noise, it can affect jitter.

[Edit: I should have also said that the noise on the power or ground is more likely to directly affect any analog circuitry.]