I don't believe that at all. DPR got busted for posting total newbie questions on Stack Overflow, after all - and SN displayed a deep knowledge of secure coding and cryptography!
What better cover?
There is nothing inherently illegal about creating BitCoin but there is something very illegal about facilitating drug trafficking. If they were the same person, wouldn't you practise good OPSEC to keep you out of prison? What is the value of keeping your identity as BitCoin creator a secret when you are in prison?
If they were one and the same, it seems to me, you would just practise good OPSEC across the board or, if need be, make "mistakes" that reveal you as BitCoin creator (and take the credit) and keep your identity as SilkRoad founder a secret.