No. For normal camera metering, exact focus is not critical for determining exposure. You can move in close to meter from the face without achieving perfect sharp focus first.

What matters more is the type of metering:

• An incident meter reads the light falling on the subject, so focus is irrelevant.
• A camera’s reflected meter reads light bouncing off the subject. If you meter tightly from a light-toned face, the camera may underexpose because reflected meters assume the scene averages to a midtone. In that case, you may need to add about +1 stop of exposure compensation for a light Caucasian face.

So: no, you do not need sharp focus just to meter exposure, but you do need to understand how your meter interprets the tone you are metering from.