There are hermits that get quite large and keeping some of them can be a hobby in itself. As long as they can live in shells no larger than the size of your thumb they should be no problem for any octopus. Hermits living in shells the size of your fist may still be octo lunch but size is always a factor in the preditory world. Be aware that not all octopuses will eat hermits or may only eat them when first intoduced to the aquarium. Small crabs and shrimp are the most often eaten common foods.