I'm not sure I see the connection between iSCSI, scinstall and quorum. Do you not have a shared disk that is directly connected to both nodes? If you are planning to use iSCSI for shared disk then, if I recall correctly, you'd need to use a software based quorum device, but I'm not sure whether it is officially supported on generic iSCSI devices.
See the manual section:
in particular, the section around "If you turn fencing off for a shared disk, you can then..." and the list of supported devices above.
Yes, iscsi is a valid option. If you have setup your iSCSI luns correctly, you can use it for shared storage. There is an old whitepaper, based on Open Solaris and Open HA Cluster, the former open source version of Solaris Cluster that goes into some details about using iSCSI. Maybe this can be of help. You can forget most of what is in there, as it has been changed with the latest Oracle Solaris Cluster 4.0 release on Solaris 11. But the iSCSI stuff may help. You can find it here:
Keep in mind that not all iSCSI storage is supported with Oracle Solaris Cluster.