Metering Electrical Energy

The short answer is 'Yes', the energy measured by a three phase energy meter and sum of 3 single phase meters should be same regardless of the load unbalance.

But …

There are two types of 3 phase energy meter: (1) three element type – the energy meters have input for currents from all three phases and (2) two element type – the energy meters have input for currents from only two phases. The three element meters are supposed to be used in three phase four wire (three phase and neutral) system, while the two element meters are intended for the three phase three wire (three phase without neutral) system. If you use two element meters in three phase four wire, then there will be difference of recorded energy in the case of unbalance. I assumed you have a three phase four wire system and make sure the three phase energy meter you mentioned here is a three element type.

See this link for additional help:

https://www.ohiosemitronics.com/pdf/tech_papers/Two-wattmeter-method(E).pdf

- MS