Answer:
Yes, it is possible to use the ADE9078 3 phase energy meter in a 1 phase energy metering application.
The ADE9078 can be looked at as 3 x 1phase meters in one device so it is possible to use them individually. Since there are additional features built into this IC for 3phase (angle differences for example), you will need to be aware of these and keep some register settings in mind below:
If phase A is used:
Enable phase A to CF output
COMPMODE register termsel1 to 4 = 001 - this enables the phases to use CF generation CBA
Set zero-cross to phase A
ZX_LP_SEL > ZX_SEL = 00