AFAIK, behind a casascius bitcoin you can find a private key of a p2pkh address (starting with "1"). Example:
i believe those private keys are in a special shorter form called mini private key format that can be found here:
https://en.bitcoin.it/wiki/Mini_private_key_formatin that case the key has to be converted to a normal WIF first then that should be imported in a wallet. casascius has some tools on github for it.