It is possible for the cluster routers to advertise an ISIS route into OSPF and overwrite the ISIS learnt routes on the peer router. To avoid this from occurring use a route map to reject routes from the peer OSPF router-ID.

R1 and R2:

route-map “reject” 1
no permit
enable
exit

R1:

router ospf
accept adv-rtr 10.255.0.2 enable route-map “reject”
exit

ip ospf apply accept adv-rtr 10.255.0.2

R2:

router ospf
accept adv-rtr 10.255.0.1 enable route-map “reject”
exit

ip ospf apply accept adv-rtr 10.255.0.1