I used to be a debt negotiator.
Basically, customers would have me negotiate with their unsecured creditors for lower payoffs. It only worked after six months of delinquencies because at that point the debts cease being an asset to the creditor and actually become a liability.
When a debt is settled it will show on your credit report as "settled in full. paid as agreed" or "SIF."
When a potential lender sees SIF on a credit report they know that the applicant did not pay the full amount and it can be detrimental to the process (regardless of credit score).
In fact, debt settlement can lower a credit score initially.
If you are 12-18 months delinquent on those accounts then SIF entries on your credit report should start to raise your score within 90 days of each settlement.
If your lender is telling you to settle maybe they are willing to overlook the fact that you did not live up to your original agreement with your creditors.
Here is a link to the FTC website explaining debt settlement:
Settling Credit Card Debt | Consumer Information