The bow hold varies slightly between the various "schools" of teaching.
My Moscow Conservatory trained instructor preferred her students to have the weight of the hand constant and even on the first finger, between the first two knuckles, and the rest of the hand as completely relaxed as possible. With this style, depending on your pinky length, the pinky may leave the stick at tip position, and help with balance and rotation at the frog position.
I have looked into other styles, and one of the common themes I have seen is that the technique should allow for the least use of muscle in the lower part of the hand so as to give the wrist the most flexibility possible.
In teaching, I have found that when students press with the pinky or third finger, it activates the thumb muscle which contributes to the locking up of the wrist through tendon action, so I actively discourage the use of the back fingers as much as possible while they are learning.