"I'm wondering if anyone has successfully kept a croton in their vivarium."

I have. I had one in my setup with green tree frogs for about 6-8 months. No ill effects that I could detect. I removed it only because it was only producing plain green leaves which they tend to do when there's not a lot of light (it was under 2 40 watt flourescents not enough apparently). It's in the living room now where it gets more light and back to producing the multi-color leaves we've all come to expect of it. Also, FWIW, I've touched the leaves plenty of times and have never had any skin irritation. I do not intend to eat it though.