It appears iSNS service is not available with NX-OS 5.2. I am on MDS 9222i with NX-OS 5.2. iSCSI Feature is enabled, but iSNS feature can't be enabled.
mds9222i# show version
...
Software
BIOS: version 1.0.12
loader: version N/A
kickstart: version 5.2(2d)
system: version 5.2(2d)
BIOS compile time: 09/10/07
kickstart image file is: bootflash:/m9200-s2ek9-kickstart-mz.5.2.2d.bin
kickstart compile time: 12/25/2020 12:00:00 [04/24/2012 18:33:58]
system image file is: bootflash:/m9200-s2ek9-mz.5.2.2d.bin
system compile time: 3/21/2012 14:00:00 [04/24/2012 20:11:09]
mds9222i# show feature
Feature Name Instance State
-------------------- -------- --------
cimserver 1 disabled
cloud-discovery 1 disabled
cluster 1 disabled
cluster_test_app 1 disabled
dmm 1 disabled
dpvm 1 disabled
extended_credit 1 disabled
fabric-binding 1 enabled
fcip 1 enabled
fcsp 1 disabled
ficon 1 disabled
fport-channel-trunk 1 disabled
http-server 1 enabled
ike 1 disabled
ioa 1 disabled
ipsec 1 disabled
isapi 1 enabled
iscsi 1 enabled
isns-server 1 disabled
ivr 1 disabled
ldap 1 disabled
npiv 1 disabled
port-security 1 disabled
port_track 1 disabled
privilege 1 disabled
qos-manager 1 disabled
san_ext_tuner 1 disabled
santap 1 disabled
scheduler 1 disabled
scpServer 1 disabled
sdv 1 disabled
sfm 1 disabled
sftpServer 1 disabled
sme 1 disabled
sshServer 1 enabled
tacacs 1 disabled
telnetServer 1 disabled
tpc 1 disabled
mds9222i(config)# feature isns-server
^
% Invalid command at '^' marker.
mds9222i(config)#
