The one he posted was definitely a vaild bitcoin address. If he input it wrong into his miner, then solo would have just rejected him entirely.
I verified the address creation and validity with a block explorer. It's definitely there and all good. I'm just not sure why it wasn't reporting on the stats page. I tried for 5 hours and got nowhere, hence reverting back to nicehash.
The status page showed everything looked good for solo.ckpool and so did the configuration page so I don't believe it was hacked.