You could meter something gray, take the meter readings you get, and set them on the camera as-is. In Zone System language you "Placed" what you metered on Zone V. That's perfectly all right.
For black and white negative film... Shadows are where the film gets the least light. If you underexpose, the shadows get ruined because they get no detail on the negative. So almost everyone who uses Zone System meters shadows and places them so they get the right amount of noticeable detail.
Developing longer, such as N+2, will move light gray closer to white. And it will also move everything else a little. Like you suspect, it will move standard Zone V gray to a lighter gray. But since every tone moved in proportion this might look natural in the print - even though it is not faithful.