I'm installing gas hot water heater. Copper (not flex) pipe to the nipple with teflon tape. Is it safe to assume that the nipples that are supplied with the GE heater are safe from dialectic (sorry if I mispelled) corrosion or should I buy a separate set that specifically indicates they are safe from this corrosion.

Is it safe to assume that the nipples that are supplied with the GE heater are safe Yes. Use the nipples supplied. Good luck, Tom