Geoff Watson said:
They can only use Ki Shout with Roaring Strike, not Great Ki Shout.
Geoff.
Thanks for the correction. The Singh Rager is now no longer ludicrously powerful, merely ridiculously powerful.

As a side question, are there any other Rages that can stack with the Singh Rager's ability? I know the Barbarian's and Frenzied Berserker's don't because of alignment restrictions, but what about the Sohei's Ki Frenzy?