I don't see anything wrong with Jesse Ventura endorsing Paul as long as he keeps the conspiracy theories out of the equation, and he focuses on what "republicans" like to hear by acting all overly-patriotic.
Let's be realistic here. If Jesse Ventura talks about the FEMA prison camps in a speech, many voters will role their eyes, and go "that crazy ol' Ventura again."
But if he says the baloney that category of people LIKE to hear, such as talking about how "great" America is, "freedom", etc.. etc.. and he follows it up with a "vote!" message, it will motive youth who normally don't vote, while making some of the "republicans" scratch their head and give Jesse Ventura and Paul second thoughts because they associate blind patriotism with how good a candidate would be.
Course, Jesse Ventura wouldn't necessarily be selling out either. Rather, he could be discrete in criticizing today's America, talking about how great the founding of America was, without directly comparing it today; Rather he could discretely criticize our modern society by solely speaking of only our liberties our founding fathers intended, without ever mentioning the present!
I believe discrete criticism is much harsher than blunt criticism. Furthermore, it will convince "Republicans" that Jesse Ventura is NOT "crazy" like they believe him to be. They believe Ron Paul and Ventura are acquainted, so changing their opinion about Ventura will change their opinion about Paul!
Jesse Ventura has an amazing voice, and plenty of Charisma. If he could take a discrete approach to what true patriotism is like, then the message will be very powerful.
In short, if he makes a simple speech about the freedom and liberty intended by America's values, it will convince people he and Paul are NOT crazy, and actually attract Paul voters!