Supposedly, he speaks in a Kansai dialect (which tends not to translate well in scans, for whatever reason). Gin also speaks with a Kansai accent, so the likelyhood of Hirako being Gin is kinda high.

I think it may also be important to remember that Aizen has the whateverthehellitwascalled so he may have transformed himself and his new vice captains into Shinigami-hollows already (that is, if he wasn't one already).

I'm not so sure the one that everyone thinks is the Gound Fisher is in fact it. I thought it was at first, but the mask changed a lot and now it has a zanpaktou. Either Aizen messed with it some more with the whateverthehellitwascalled (or it got even more power from whatever altered it in the first place).