Is it a violation to refuse to let the OSE officers in to my property ?

It is a violation of the HAP contract to charge more rent for voucher recipients than market rate tenants.

Which one would also have the resources to challenge Airbnb if Airbnb threatens to delete their brand due to violation of their TOS? 

Make sure it explicitly explains the process for termination if you are unhappy with their services, especially if they violate the terms of your agreement.3.

If you see someone violating the rules, create a post with "@moderators" and we will receive a notification and respond.Again, welcome to BiggerPockets and happy investing!

I ended up evicting him because he continued to violate the no-pet rule.  

They are violating your constitutional rights and probably violating the takings clause.

To give you an idea of how we approach it, we assume the worst-case scenario right from the start is 9-12 months of no rent, $5,000 in legal fees, and an additional $5,000 in expenses to deal with moving their stuff, putting it in storage, and dealing with health code violations or NOV's from the city during the process. 

Four violations and you still think they are "sweet" pets?

One inspector in Ramsey bragged up on media how he is actively hunting for violators.