I guess the owner would have to weight the cost vs benefit.

My apologies @Chris Seveney, I failed to mention you in my previous reply but I see where you are no longer interested in the area. 

If they fail to allow access, they are charged a $100 trip charge fee.If their schedule doesn't allow them to be there, then I will open the home for the contractor.I try to respect the tenant's schedule, but I also expect them to respect mine and the contractor's.

The seller failed to pay bird dog.  

Can I cut the glass, etc. in place to remove the majority of the weight, and then I'll just have the frame to remove? 

About 90% of the time they fail to meet HUD guidelines.HUD guidelines require that to qualify as an Emotional Support Animal, the prospective resident must have a letter from a licensed health professional, licensed in your state, in which the health professional acknowledges they have a relationship with the client that was more than just one session. 

Looking at a HUD home where the pressure test failed for the plumbing.

In which case you need to ask yourself, do you know all the issues with this property and why do you think you could succeed in turning this property around where this operator has failed.

If I can't find previous owner (building was forclosed - so seller was the bank), and all my efforts to find and talk with him have failed - why would the judge believe me over tenant?  

You'll want to understand what kind or notices and documents you need to get executed to either up their rent or turn the unit.Solid long term tenants are worth their weight in gold in my book so if theres a way to up the rent and keep them happy I's say thats the best route personally.