This is an old question I stumbled on but I think Nate Eldredge's post is misleading. Actually he gives two quite different answers why the Amendments should not apply (fyi, the confrontation issue you mention would be covered by the 6th not 5th amendment, though double jeopardy falls under the latter.)
The first given answer is that the proceeding is administrative,
"The Fifth and Sixth Amendments are about civil and criminal court proceedings. They do not apply to a university's internal disciplinary procedures, which are the subject of the Dear Colleague letter."
and second is that none of "life, liberty, or property" is implicated:
"A university's disciplinary procedures do not deprive anyone of their life, liberty, or property. Typically, they only decide whether to suspend or expel the person as a student at the university, or apply other academic punishments (failing grades, marks on transcript, etc)."
It doesn't really matter, though, since both are wrong as stated, the second egregiously so. As to the first, due process has for decades been held to apply to administrative proceedings, not just crim/civil trials. Generally the level of protection is lower, just as the due process protections in a civil trial are generally lower than in a criminal trial. You can look up Supreme Court cases like Goldberg v Kelly and Matthew v Eldridge to start learning more. Generally the protections do include a right of confrontation.
Second, "life, liberty, or property" are certainly implicated when someone is expelled or suspended. These are abstract terms; you cannot hope to understand them literally, and must look to how they have been interpreted in case law. Think of analogous situations to see how crazy the proposition is. Could someone be kicked out of the military by his superior, with the only reason offered being "I kicked him out because I was bored"? Clear due process issue, once you see how the Court has defined "life, liberty or property." In this particular context, look up Goss v Lopez, requiring due process when public high school suspends a student, or Perry v Sindermann for due process rights in a university tenureship case.
So if confrontation, at least, is required, are these colleges all guilty of due process violations? Well, these due process requirements will only bind public universities, since the amendments are only binding on the federal/state governments. That is the real reason due process rights can be violated by most universities--they don't exist, at least when the university is private. They certainly exist when the university is public, but frankly I don't know enough about the Dear Colleague letter in question to say if/how it has been challenged by accused students at public universities.