We just had the Katana Ganma returning in the first part of the Ryoma two parter. Also, Shimamoto Kazuhiko, the monster designer for the Ganma, confirmed in his twitter that they have a "great person" motif too, like Ghost himself.
The odd thing is that even though in the tv show they avoid referencing the historical identity of the Ganma, only referencing them by the possessed object, during his return episode, the Sword Ganma used Sasaki Kojiro's personal technique, which confirmed in an obvious way some people's speculation about his identity.