Yes, marimo carpets are done similar to ricca carpets, cut up marimo balls are tied around small stones or affixed with stainless steel mesh and they eventually grow in. They give a really nice 'rolling hills' effect. I was just considering peacock moss because I have it on hand. It all depends on if I can find stainless steel mesh.
the slope isn't that steep, I'm confident that with the addition of the moss covered stones it will be more stable. and it's been holding just fine so far.
edit: Oh, caught your edit about the cherry shrimp, I was considering it but I've had cherry shrimp in a similar vase and they didn't do so well, so I think this one will be livestock free as well.