300.5 (I) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors shall be installed in the same raceway or cable or shall be installed in close proximity in the same trench.You can read the code section that applies to say that you can't use a separate EGC with the USE cable, or that you can.
All of the circuit conductors would be in the same trench, but would not be in the same cable. It is my opinion that the separate EGC is a violation of this code section.
this language seems close to 300.3 but the last section starting with the word or shall be installed may give some wiggle room, (just a thought)