Even if a tradeline (like BML) doesn't report show your credit report it still must be disclosed on the mortgage application. They require you to list ALL your outstanding debt/monthly payments and you sign a statement saying you have disclosed everything. If you choose not to disclose outstanding balances and they come to light later the bank can accuse you of mortgage fraud and either stop your loan in it's tracks or call it after it's funded.
In short, BML and other non-reporting tradelines won't effect your credit score but they will still count towards your DTI because you are obligated to tell the bank about them.
