Hello,
There is no Specific Document that states "Symantec Endpoint Protection RU6 MP2 do not block flash drives on 64 bit OS. """""
However, Brian81 pinpointed at a proper document which states Device Control feature of Symantec Endpoint Protection does not work on 64 bit machines.
Again, question arises why would Symantec Endpoint Protection block flash drives i.e.; until and unless you have created a Device Control Policy to Block Flash drives.