Wanting to glue together multiple iscsi targets is a perfectly valid idea. There are plenty of reasons you'd want to do it.
Here is a simple scenario:
1) I've got 2 servers, and each has 12 disks in a Raid6, giving me 36TB usable space on each server. All of that storage is already RAIDed, to provide redundancy and protect from disk failures etc.
2) I want to setup one server with an ISCSI initiator that connects to all the targets, and then use LVM to glue the ISCSI volumes together into a single 72TB volume, with a single 72TB filesystem. To do that, i should be able to use LVM to join the 2 iscsi volumes together into a 72TB volume and format with XFS.
3) When that 72TB filesystem is full, i want to be able to get a 3rd server and have it export another 36TB ISCSI disk. Then, on my master server, which is running the initiator/LVM, i connect to the new iscsi disk, setup an LVM physical volume on it, add that PV to the pool, expand my 72TB LV to 108TB LV, and then XFS allows me to easily expand the filesystem into the new space. Easy.
Basically, this should be an easy way to aggregate fragmented storage across a number of servers, to provide a very large filesystem.
The whole point of iSCSI is that it is supposed to present a remote SCSI device as a local one. If it is OK to use local disks in a RAID, it should be OK to use ISCSI disks in a RAID.
If i temporarily pull a disk out of a hardware RAID0 with no redundancy, i do not lose any data on that RAID. EVER (assuming a properly journalled filesystem). The RAID just goes offline. And if i put the disk back, then the RAID is back online. And it should be no different for a RAID of iSCSI targets.