Yes you can run 20/4 in veg.
I've done 18/6, 20/4, 24/0, 12/12, 11/13, 10/4, etc... The only thing I've noticed is that 11/13 and 10/14 can help long flowering sativas finish faster.
I don't believe anyone that says they realized a 30% increase in yield going from 18/6 to 24/0. If they're making claims like that then they need to provide proof that they grew multiple plants of the same strain in the same conditions with the same lighting. A minimum of 5 plants for each light schedule preferably 10 or more. The only difference should be the 2 hours difference in light hours. Without that it's just talk.