I do not have the Electrial Power Suite so I cannot comment on its suitability. In addition to posting here, there is an Electrial Power Suite on the Forums, although it gets very little traffic. Some of the NI people involved with the suite seem to monitor that Board.
Assuming that your customer has suitable instrumentation and data acquisition hardware, it should not be too difficult to measure/calculate phase angle with LabVIEW and standard DAQ drivers.
Can you be more specific about the equipment?
Lynn