No, they don’t usually eat their waste poops.
They eat a special type of poop called caecotrophs which you should never see in the cage - they take them directly from their bottom.
If you are seeing less poops in the cage, then it’s possibly because your piggy is not eating enough hay.
The only way to tell a piggy is eating enough hay is through the weekly routine weight checks. Hay is their main food but you cannot judge they are eating enough by eye.
If you become concerned about your piggy you should switch to weighing them daily so you can more closely monitor hay intake.
Poop output is 1-2 days behind food intake and that delay means that by the time you notice less poops, then a piggy has not eaten properly for a few days and could have potentially lost a lot of weight and be in need of medical assistance and syringe feeding.
This is why weight checks are essential, they give the only accurate, real time information on hay intake.
Have you been weighing your piggies weekly?
Weight Monitoring and Management