I don't think he's "sneaky".  Trying to work out who's connected to what is pretty much standard for any investigation.  pirate pass-throughs were listed on GBLSE, so the role of both the PPT operators and GBLSE itself in pirate's operation is bound to come under scrutiny.  Even seemingly unconnected things could be connected, so no investigation is going to dismiss information about other apparent ponzis or enterprises in which the operators have "cut and run" out of hand just because they're not connected at first glance.  They're going to look for any common points and common people.

I think that anyone who looks like they can provide key information which may be vital to a future prosecution needs to realise that they may find themselves on the receiving end of a subpoena at some point, though, and that those who facilitated the flow of funds to pirate probably have the most to worry about in that regard.  

pirate's venture was being openly promoted here when it was thought that he was laundering funds for Silk Road or other illegal enterprises, so there are larger issues involved than him simply operating a possible ponzi.  To an investigator, this place must look like a haven not just for scammers, but also for those looking to attract funds for and from other illegal ventures.  Any investigation into pirate's activities is going to raise questions about other people and other ventures which promote themselves here - that's a given.