Hi Chetan,
Let me clear some more information version wise.
12.1 RU1 MP1
We have no issues while Deploying client through SCCM OSD task Sequence, only reboot issue as I mention in the below link
https://www-secure.symantec.com/connect/forums/sep-client-install-through-sccm-os-deployment-task-sequence
12.1 RU3
SEP client installation falied when we deploy through SCCM OSD task Sequence. Please find atached install logs. (this installation on fresh PC , SEP client installed during the OS installation).. I found some errors from Install log, and I found the below article for that error , but we are not using the windows defender .
http://www.symantec.com/business/support/index?page=content&id=TECH205042
still we didn't check the reboot issue, because client is not installed .
When install teh same package manually , installation was success.