First before they start machining your engine. You should first ask how many VG engine they have worked on. Are they familiar with the Nissan engines. Specially the crank, piston clearance etc. Make sure they know what they are doing. Are they cleaning up deburring the water / coolant galley?
Clearances are critical. If you trust him. Then go for it. Otherwise, it will be sad to see your engine with a spun bearing or other problem.