its fine to have moss in with them as long as u feed in a seperate tank,i like feeding in seperate tanks as to not have any chance of causing impaction,but he'll be fine,also have you done any research on him whats ur temps and humidity for day and night
Should be fine!
I mean think of all the time a frog or toad must accidently swallow pieces of leaves, dirt, and all sorts of debris that come with their pery when they eat them! I'm no frog expert but logically they should capable of managing a piece of grass, moss, or a little piece of twig once in a while! Though they tend to use their font paws to remove large debris from their mouths, they don't exactly wash their foods thoroughly before eating!