Is teflon tape acceptable on natural gas threaded pipe joints for a water heater?

Yes, but it has to be wrapped clockwise on the threads. I use pipe dope that has teflon added to it and never had any problems.

Yes and no.

You can use teflon tape but it must be teflon tape that is rated for gas use.
The white stuff off the shelf for taping water joints is unacceptable.

As Plumber Tom mentioned, the simplest solution is to use pipe dope rated for gas instead.