I concur. I understand the ethical conundrum of not wanting to use the rate if you're not on official business, I've dealt with that before. But it's truly on a case-by-case basis.
@WVMomof3, you might direct him to the horse's mouth:
Who is Eligible for Marriott's Government Rates? Marriott for years has explicitly stated in their T&C that federal government employees are welcome to stay at their properties on the official government rate even if it's for leisure travel. Now, I always double-check the terms of the rate for the specific hotel I'm booking, because the hotel can disallow leisure use of the rate if they so choose. It will be in the terms of the government rate at the time you book - you won't be caught by surprise. I've even had hotels ask me at check-in if I'm there for business or leisure, and I'm always honest and answer leisure. It's never been an issue.
From a legal perspective, you are free and clear to use the discount as well. I'm not sure what your DH needs to see to be convinced that it's legal, but this has been reaffirmed by ethics and OGC offices government-wide over and over again - we are allowed to take advantage of discounts offered to
all federal employees as a group, provided that the discount is ordinarily always available and we are not being offered the discount on the spot as a result of our standing as a federal government employee. A quick Google search brought multiple results affirming the law, but here's one such link from USDA:
USDA Office of Ethics. This is another one from
OGE, Office of Government Ethics. The writing clearly states that government employees are allowed to use the government rate for personal use as long as the hotel (or even car rental or other things as well) affirm that it's ok with them (but obviously you cannot claim to be on government travel just to get the rate).
Other hotel chains are not quite as explicitly government-friendly as Marriott. When I'm booking a cash rate, I always choose government first, and read the terms. Often, it's not allowed, and I book a regular rate. As I recall, Best Western is usually very solid in allowing the discount, but the rate is often worse than the best available public rate. Hilton is very hit-or-miss. Wyndham and Hyatt rarely allowed it. It's been several years since I've booked a non-Marriott hotel on a cash rate thanks to churning, so chances are a lot of this stuff has changed.
But yes - show him the legal links! No need to pay more than is necessary.