Of all the worlds one would expect to find the Order of Revan's plan unfolding, Rishi would hardly seem a likely candidate. While it's true that the island-dotted paradise would be ideal for planning without fear of interference, the lack of Imperial and Republic presence would also limit the ability to act on those plans. That is, unless the Empire and Republic were somehow drawn to Rishi.
The Nova Blades were employed by the Revanites to trick the galactic powers into believing their most vital fleets were at the mercy of the pirate gang's infamous hyperlane raids; in reality they were being corralled into a trap. With a signal jammer taking away their ability to communicate with one another and with their ships compromised by Revanite traitors, Darth Marr and Master Shan--and the many thousands under their command--now stand on the brink of annihilation, just as Revan had intended.