PEX to hot water heater

[RossPH]

can PEX be connected directly to an electric hot water heater via a brass 3/4" IPSF to 3/4" PEX fitting with Cu crimp ring?
I think the heater will have plastic heat trap nipples.
This is in N.C.
Are the flexible Cu connectors just for fuel burning heaters where the PEX may be near the hot flue?
If needed  Why?  and how long
An advantage of PEX is the energy savings.
I am an "energy nut" and want to minimize the distance the Cu will conduct heat.
On the same note: Can PEX be used on the T&P relief valve to avoid heat conduction loss?