Their thinking is that if someone wants to sell with the aid of another party, just engage a realtor.

IF your MLS doesn't include the owner information, then you have to get it from a third party.

If it's a good deal for all parties, do it.

The lease was signed by all parties back in July 2019.

Data inside the Blockchain is protected by a cryptographic hash function making it immutable.The systems and the critical parties involved would be able to communicate in real time.

In order to get the best interest rate on my refi (this is a BRRRR deal), my loan company has now told me that I am required to get a document filled out by a 3rd party property manager.

If you go to a rubs (Ratio Utility Billing System) situation where a third party is issuing the bill that probably would work.

A partnership generally requires the parties (at east two) to carryon a trade or business and implicates the sharing of bottom line profits and losses.Based solely on the above it sounds a little more like you are being compensated on a one time basis for services rendered rather than as a partner sharing in the profits and losses of a partnership. 

I recognize that a third party appraisal will need to happen for the current value.

In any case you need consent from both parties.