Three phase motor current verification
Essencially yes.

To determine the power flowing into or out of a 3phase system you can make use of 


1wattmeter method
2wattmeter method
3wattmeter method


In this instance you could take advantage of this and assume the 3 currents are the same (bar phaseshift) to derive the currents of the 3phase system.

HOWEVER... you are interested in Iq which means you really need to know all 3 currents and equally the present angular position to then apply park&amp;clark transformations correctly.

Any slight disturbance in the other 2 current waveforms would influence the actual Iq used by your FOC, something you would not be able to see.

For a CRUDE 1st approximation, yes you could take the one and phaseshift it to produce the other 2 waveforms