From the FAQ:

Archaeology pets are not included in Rarity
The only archaeology pet that is considered actually rare is the Crawling Claw. However, this item has a problem because it shows up in your archaeology journal as Mummified Monkey Paw. At this time, Rarity does not support archaeology detection for items whose journal name differs from the actual item name, so Crawling Claw is not available for detection.

Is this still a problem? Perhaps we can get around it somehow? I haven't bothered with Archaeology, but perhaps someone knows.