I have been doing this for a while. With one Drivepool, I have 4 pools and 3 of these are using iSCSI disks on different PC's. Because I have configured each pool to only uses disk on a single PC, it is easy to seperate the pools.
As Drashna says if a complete pool is not available, Drivepool does not know about it, but as soon as one of the iSCSI PC's is powered up, the iSCSI link auto reconnects the disks in a pool, and the pool reappears. I use these iSCSI pools for archiving and backup. Prior to using iSCSI, I used eSATA to add external drives but at that time I did not have seperate