Finally had some time to experimnet with this, probably won't give any new insights, but anyway
DGing gives the DGer speed and takes speed away from the rest of the team. That's not so bad for the people on the side of the DGer if he survives, because the DGer will effectively protect them from all enemy attackers on that side.
The other flank, including the center, has to compensate. If they're prepared, that's not so bad. They probably won't have enough speed to attack or block the enemy attackers all the way to the rim, so they'll have to either fall back to the zone and block there, or stick around in the middle, waiting for it to open up. The DGer will leave holes to slip through, whether he does his job or not.
Meanwhile, to be useful, the DGer absolutely has to kill some, I'd say at least two, enemies on his side. One, to pave the way for his teammates to roll into the enemy zone, and two, to leave the nasty dead man's trail end sticking into the enemy zone to make the defenders life miserable.
The biggest problem there is this: if one of the enemies on the DGer's side breaks early, the surprise attack fails; breaking early effectively counters the DGers speed. If all of them break early, the DGer can't even kill anyone. And the problem with that is that the enemies can (potentially, it needs a keen eye) see you DGing and break early as a reaction, however the potential DGer can't see the enemies not breaking early so he knows a DG will be effective, because it hasn't happened yet.
I'd say, therefore, that against a team that knows what it's doing, DGing isn't an effective tactic. There is an effective counter. Luckily for the DGers, on CVS Test this usually isn't the case
If you observe that your flank of the enemy team breaks late, you can expect to be able to surprise them with a well timed DG. Don't expect it to work more than two times in a row, though, and don't surprise your own team. Have two instant chats, one for DGing on the right, one for DGing on the left.