Are there any cheat codes for Hellfire, such as getting more gold or summoning certain items?

I don't know if they work for Hellfire but there are tools you can use to increase gold and stuff, but no codes.

Sadly, the normal dupe method from Classic Diablo does not work in the Hellfire Expansion.
I have not tested whether the Bobafett trainer still works - neither in Classic Diablo or in Hellfire.

You aren't right classic dupe method item using 1g in full inventory working well for both Diablo and Hellfire. I have tested it yesterday. But 1 thing doesn't work - that's you can't dupe gold because it will be dropped to the ground but any item duping well which you could just dupe and sale to get gold.