No, the Corsairs are neutral to Kusari, and should not be pirating there, Corsairs should only be in Kusari when smuggling artifacts to the Hogosha.
Corsairs ARE allowed to pirate in Bretonia, Rheinland, the Omegas, the Sigmas and the Omicrons, which covers about half of Sirius (so you have plenty of choice on where to pirate).
Let's be clear, it is not against server rules for a corsair to pirate in kusari or the taus, but you will face inrp consequences from the Corsairs and the Kusari for breaking their inrp laws.