You can ferment pellets, you can ferment whole grains, or even a mix of the two. If your pellets contain probiotic strains, it may end up smelling more like yogurt, than like yeast. That's exactly what happened when I fermented my girls' pellets. Either is fine to feed, but always smell it before you feed, in case it's doesn't smell like either of those things. If it does smell like something else, it may be really "off", and upset their digestives. Also, you should always make sure the water comes over the top of the fermenting feed and there's no mold. I used to ferment a bit, but I've since gone back to dry pellets. I may start it again at some point.