I haven't found a debt hardship letter to be that useful for my first mortgage. They just want you to call HUD or provide them with a long list of documents in an attempt to modify the loan. And you can get that far on the phone, without a hardship letter, at least in my experience with Wells Fargo.
However, my HELOC lender did acknowledge my hardship letter, but really still made little difference. All they want right now it to verify my income through 30 days worth of pay stubs, 3 months bank statements and 401k/investment accounts (as if I have them), and a list of all expenses or a budget. The don't seem to take the hardship letter at face value and want to verify what you tell them. That's understandable.
But I'm very weary of providing this information to a creditor who at the beginning of the call says all inform gathered will be used to collect a debt. It's actually a conflict of interest. They want to help you keep the house, or they want to collect the debt. Hard to do a good job at both, and I think their much more interested in collecting the debt or an advantageous loan mod for the bank.