Auto ISO for shooting videos with DSLR
It depends on what you are doing, but generally for video you want pretty tight manual control to avoid changes during a shot.  What I often do when I'm in a hurry (and don't want to determine optimum settings manually) is to let the camera figure out what it wants for settings and then manually enter those.

That said, while changes in exposure during a shot can be very distracting, it's still better to get the shot than not get it, so occasionally I may shoot with the camera fully on auto and use exposure compensation as necessary to adjust the exposure.  This can be particularly useful for live events where you don't have time to adjust manually.  Note that if you are shooting with multiple identical cameras however, it is best to lock everything down (including white balance) to ensure a consistent look between cameras.  

Ultimately, there isn't a right answer, just be aware of how distracting changes in exposure can be during videos and balance the need to have the camera adapt vs the need to control when and how adjustments are being made for the content you are shooting.  It's best to try to avoid uncontrolled changes, but not at the expense of not getting a shot.