Can I measure Rho Overall in Modulation Accuracy of the 1xEV-DO forward link signals, because it was available in my PSA and/or E4406A VSA with old...

Yes. Please check the measurement setup menu to add Rho Overall result in Modulation Accuracy.

[Meas Setup] > {Advanced} > {Rho Overall On|Off}

Because of 3GPP2 conformance requirements change, it was turned Off from the default measured results in PSA firmware revision A.09.18 and later and E4406A VSA firmware A.10.06 and later.