The actions of university police are very dependent on how they are set up. There are two categories:

1) Those that are glorified private security firms

2) Those that are actual police with authority to arrest and investigate.

If you go to a school with type (1), they are much more likely to violate these rights as they have no real investigative authority outside the university judicial system. You can sometimes have issues with (2) if they know they will just be referring your case to the internal university judicial system, but they are often more professional in getting any evidence cleanly.

You are not being tried in a court under the ruleset of an individual state, the fed, etc. You are under the prosecution of a private entity and their private police force, which has no obligation to follow rules of state run police.

The only reason they should care about the law of the land is when they themselves are violating it, and there is no law that says "all private police and prosecution must also abide by innocent until proven guilty".

In a real court, refusal to allow a search doesn't create probable cause and it can't be used against you.

But colleges don't follow due process.

I'm under the impression that campus police departments were mostly set up by late 1960's, and that is when they established their current ways of working.