Well first of all, how many DC trainees have you seen with good calves? The only two people I know that follow DC training is Dante himself and David Henry, both of which are not exactly known for their calf development.
My opinion is that it is more important to spend the time under the weight stack working the contraction of the muscle in order to get size. While stretching is important, lets face it there are tons of guys out there with good mass who don't stretch at all, any body part. So rather than advocating no stretching, I say do it at the set is over. After the last rep you can then stay under the pads and force stretch the muscle to make it grow, but doing so during a set only compromises the total effort you can put into your contractions.
Overall my opinion of DC training is a mixed one. I have tried it and it doesn't work for me. Actually I don't think it works for most people as a majority. It is a nice break from standard training that allows for more rest which may attributed to DC training while in fact that is only indirectly. Most people simply can not generate the all or nothing mentality to do one set to utter failure. And those that can risk severe joint and tendon injuries that are common place with super high intensity sets. Look at Dorian, while not exactly DC style he employed the one set to failure that DC uses as a foundation. Instead of rest pause and static holds he did negatives and strip sets. And cropped up injuries left and right.
In light of direct calf training, there are not many people on the pro scene today that really have the eye popping calves that were rather common in the late 80s and mid 90s that were sported by Dillet, Paris, Stewart, Demayo, etc... the ones today with good calves are Branch, Priest, Vince Taylor (throw back), Mustafa, and a few more. And none of them train DC style. And if you were to see them in person training most will be training only the upper portion of the movement (and in sloppy form)