It is possible that pirate from BS&T is Dread Pirate Roberts from Silk Road.  This would explain why he's got to keep so quiet about what he's doing with the invested coins.

That would mean it's not a Ponzi; it's simply profiting from the Silk Road mixer service.  Assume that that this is the case.  It would mean that BS&T is not a scam.  It doesn't mean it's risk free though.

Now, the feds will be looking to shut down Silk Road, and it's certainly not beyond their ken to make this same potential link as we have.  pirateat is leaving IP fingerprints around the place for BS&T... enough for a fed to physically find him (they're good at finding people from IP addresses).

That will then let them shut down Silk Road, but more importantly, will leave all the BS&T investors with no access to their investment.

The other possibility is that it's a Ponzi.

Not sure either of those have a good risk profile.