Not necessarily. VPs don’t have a lock on the presidency. A VP candidate is there to help get the nominee elected President. That is the major criteria for a VP nominee. If Paul helps bring in indepedents and get Cruz elected I am fine with it. He would never be elected President so I am not worried about it. Even if he did get elected somehow he would be better than a Hillary or an Obama
Choosing a veep is choosing a president, that is the accurate and proper assumption, does it hold true in every case? no, but it is the proper assumption, if you want to keep someone out of the presidency, you would not want to make them vice president.
On the other hand, if you have a favorite who couldn’t quite snag the nomination first time around, there is no better place that you would want him, than being vice president.