I have tested your scenario with a BTSX and was able to reclaim it with just the private key on a brand new wallet. Once the key is imported you'll need to execute regenerate keys and rescan the blockchain. I think some of this is triggered automatically now. None the less; a WIF from the CLI key gen tool works fine. Though to be honest I have a pub/priv key created this way but I haven't had the stones to send large amounts of money to it yet. I know it works, I've tested it a few times...but...I don't know. It's a mental block.