LOL, they will NEVER tell you that it is EOL or about to be. If they did that, they would lose sales. Sales people lie, remember that.
That said, BE as far as I know only goes by ONTAP versions. If the StoreVault uses something other than ONTAP, then I think there is your answer. But ONTAP 7.x running NDMPv4 is usually what Symantec wants to use for most flavors of BE.
While you've talked to NetApp, what has Symantec Support said to this issue? Also not supported, go back to 11?