Because of the financial crisis, bank lending to small companies and private lenders have decreased and their risk exposure has shifted to larger companies and corporations. This lack of lending diversity creates a larger risk for banks when a particular sector get hammered like energy is now. There will be banks that have a lot of exposure to energy that will be hurt by this, especially if low oil prices stay at this level for a while.
They won't be bringing in as much revenue so it might hurt the banks. They could bring in more though, since I know that people will buy more now that it is cheaper. I guess we shall have to see what unfolds in the future for the banks and gas prices.
While glut of oil in the marketplace, and the resulting drop in the price of crude oil is putting pressure on the some bank's commercial lending operations in the long run falling oil prices are chance for banks to balance out their loan portfolios by getting rid of some their riskiest loans in the secondary marketplace with pressure from the Feds.
No, falling oil prices will not hurt banks, because with the falling prices, people will have more to save than they ever have before. If I can fill up my car for $30 instead of $50, that's $20 in my pocket that I can put in the bank. A little adds up over time, and this will be good for the banks.