Can the user performs DC voltage measurement with two recorder outputs simultaneously on P-Series Power Meters?

Yes, two recorder outputs can be used simultaneously.

Kindly configura the setting from front panel of P-Series Power meters:

To measure DC voltage from Channel A, press "Meas", go to "Feed1" and select "Ch A", then set "Rec o/p" to "1".

To measure DC voltage from Channel B, press" Meas", then select "Meas Select",go to "Feed1" and select "Ch B", then set "Rec o/p" to "2".