What about those elitely sought after credit cards and tradelines that are hidden? Like BML and I think there's a Chase one... Not disclosing any debt you have associated with those would be similar to not disclosing a mortgage that doesn't report on your CR... But no one critiques people who use those tradelines to hide their debt before applying for other credit.
It's certainly a bit shady not to admit to the mortgage, but there are many ways to look at it - things are rarely black and white.
For example you said "our" and "we" so if you're applying for separate credit products (not joint) you could always explain that the mortgage is taken from your other half's income, or only half of the mortgage comes from your income - since applicants are supposed to only include their personal income now instead HHI (which irks me since things like Medicaid/other medical assistance from clinics and gov. assistance are based of HHI still even if unmarried), why should you both have to claim a full mortgage/rent payment if you're both employed and contributing to expenses?
I agree that it sounds pretty unethical to me. I mean, if you have to ask..