Some cameras can detect or even remember named faces, but based on the answers, they generally do not seem to write standard XMP face-region tags directly in-camera.

Examples mentioned:

• Canon PowerShot S110 can recognize saved faces.
• Panasonic DMC-FZ200 can store and edit face-recognition information in playback.
• Nikon RAW files can contain face-detection data.

However, the tagging you want in standard XMP appears to be more commonly added by software after import rather than by the camera itself. One answer specifically notes that Windows Live Photo Gallery can perform face recognition and write XMP metadata. Another mentions seeing tags in Lightroom after import, but that does not clearly prove the camera itself wrote standard XMP face tags.

So the practical answer is: cameras may store proprietary face-detection/recognition metadata, especially in RAW or maker notes, but if you need Microsoft Photo or MWG Region XMP tags, you should expect to use desktop software to generate them.