No, it is not fraudulent at all: the tenant's contractual obligation (because that's what a lease, whether written or oral is: a contract) to pay rent is completely disconnected from the landlord's obligations to pay taxes or mortgage, the same as the tenant's employer must pay the employee his or her paycheck even if the tenant is then cheating on or not paying income tax. One person's performance of his/her obligations does not affect another person's obligations.