A pet shop guy said that corycats, bristlecats, apple snails, rosy red minnows, white cloud minnows, bettas, neons and freshwater batfish all do well with goldfish. Is this true?

Not really.

Cory catfish and bristlenose plecos may suck on goldfish.
Goldfish may eat white clouds and neon tetras when the goldfish are mature.
Bettas may rip the fins of the goldfish, and the goldfish may bother them.
I don't know much about batfish.
Apple snails may be okay with the goldfish as would any rosy reds or white clouds that were large enough to not be eaten by the goldfish.
Goldfish like it cool which the apple snails and minnows can tolerate but the other fish like it much warmer than goldfish like it.