Finally, I have been successful in installation of iscsitarget-dkms module on OMV 1.3 with Raspberry Pi!
I downloaded iscsitarget-dkms_1.4.20.3+svn490-2ubuntu1_all.deb from Ubuntu mirror and installed it with 'dpkg i'.
Code
root@raspberrypi:~# uname -a
Linux raspberrypi 3.12.28+ #713 PREEMPT Fri Sep 19 16:43:32 BST 2014 armv6l GNU/Linux
root@raspberrypi:~# lsmod | grep iscsi_trgt
iscsi_trgt 109732 0
root@raspberrypi:~# dpkg -l | grep iscsitarget-dkms
ii iscsitarget-dkms 1.4.20.3+svn490-2ubuntu1 all iSCSI Enterprise Target kernel module source - dkms version
But still ietd complains and will not start.