Yeah, rabbits as a species are not only tolerant to eating their own poop pellets but also gain calory extraction benefits from it. Usually mammals don’t completely break down food they eat, ie there is still energy to be gained from it. Microorganisms have the necessary biochemical pathways to do it but for mammals it’s not efficient.

Basically animal has only a few ways to into crease its energy budget. First it can simply eat more or more rapidly. Second it can find ways to make use of resources that are less contested (think of a giraffe reaching for the top of a tree or a koala being able to digest eucalyptus leaves). Third it can simply be more efficient: that’s the slow metabolism of a sloth, but also a rabbit eating it’s own feces alongside fresh food. It’s basically an evolutionary strategy to extract more energy from the environment.