Can anyone give me a good example of situations where the Fed and FDIC's regulations differ. Some bankers seem to have trouble grasping that it *is* important to get your citation based on your regulator!

Not currently a thing, but i remember the Fed being the only prudential body to be ok with balloon loans in regards to HPMLs for awhile.

It's been a few years and i forget all the details (since ATR and QM rules, and CPFB ownership sort of makes it all obsolete), but there was a FRB letter on the issue that Fed banks relied on and everyone else couldn't.

Off of the top of my head:
The Fair Housing Act (Equal Housing Lender vs. Equal Opportunity)
Some interpretations in Flood - especially the timing of the notice.

I think there is the occasional issue that applies to one without a corresponding requirement applicable to another, like this:

12 U.S.C. Sec. 376 says, Rate of interest paid to directors, etc.
Sec. 376 [Federal Reserve Act, Sec. 22] No member bank shall pay to any director, officer, attorney, or employee a greater rate of interest on the deposits of such director, officer, attorney, or employee than that paid to other depositors on similar deposits with such member bank.

If its a nonmember bank, is there any corresponding requirement?

Nonmember banks could be subject to a similar state law or regulation, but I am not aware of a corresponding federal rule for nonmember banks.