I just read this on the VMware site.
iSCSI port binding in ESX/ESXi 4.x and ESXi 5.0, 5.1 and 5.5 does not support routing.
And if you look under "When not to use port binding" on this page
VMware KB: Considerations for using software iSCSI port binding in ESX/ESXi
So it looks like that is the problem so the question is how do I get around it or add the storage without using the bonded ports if possible?