I'm less comfortable with two of those seven-footers than you are with Dooling. Dooling is a proven veteran who can handle the ball, play good D, and make shots.
In my mind, Dooling is pretty much the guard equivalent of Jason Collins. I cringe when we have to depend on him to make shots. The difference is, if Jason Collins fails to perform, then he'll be competing for mop-up minutes in the big rotation with Jeff Green and Fab Melo.
Plus, when Bradley comes back, we'll have a logjam with six guards that should all be getting minutes (the five I listed before plus Delfino) and only a four-man big rotation (KG, Bass, Wilcox, and either Sullinger or Collins). Also Green doesn't defend like a big.
It's a logjam only if you actually have good players. I don't think Dooling will (or should) ever get off the bench on any team that vies to contend for anythign unless there's an emergency (and known months-long outage of your start SG isn't one). Also, the alleged logjam will be alleviated by running lineups withere Delfino or Lee slide into the SF spot with Green at the 4.
Also, Sullinger figures to be a major piece of the rotation, not someone who will compete with Collins for mop-up duty. And regardless of whether or not Green defends like a big, Green will see minutes at the 4.