Or do I let it slide and pretend like I never saw it?

It's a lot easier to make a case for discrimination if you let one person slide for something but not someone else.

I never enter any job site or work location without wearing safety boots, safety glasses etc.

Even when I was a resident manager, if I socialized in any way with a tenant - become a walking buddy, go have a glass of wine, etc., they always, without fail, wanted some special favor and I'd have to say no.  

Trust me when I say this you need to be firm in your biz and stick by whatever rules you have made, I am the "good cop" in our biz and I usually have pity on some that tend to need housing but cannot afford the property, guess what when you let some rules slide you have made up with this forum from folks that have been there and done that, you will put yourself in a bad predicament more often than not.  

As for the hot water tank / HVAC pans, it depends, not required that I know of, but if you want one you can go buy it and have anyone install it, just lift the unit up and slide it under.

See slides 4,5,6 - As my original post suggested, its of course state specific, but in certain states and municipalities, section 8 is considered income for purposes of discrimination.

And now I'm concerned that my lawyer let this slide at the closing table.

There was already some pet damage so I wasn't willing to let the violation slide. 

Your job is to not let them prioritize cigarettes or lottery tickets or pedicures or whatever over paying you.Next time, you won't let anyone slide.