Possibly the second hardest race to nuke and to do damage to due to their automatic healing and overlords(overlords are less of a problem). However in another aspect the zerg are also extremely easy to nuke if u know how to.
The best way to do critical damage to the zerg is to use 2 nukes, this may take time to get due to tech and d and offense, once you get the 2 nukes comsat a good location to drop and nuke. Make sure u cloak ghosts before u drop them makes it a lot harder for ppl to find them plus they won't attack right when they come out. Once you have everything planned out get a dropship 2 ghosts 3 meds and a science vessel. Use the meds to blind any overlords in the vicinity so they can't spot you, then "paint" the target buildings if they rush overlords use that science vessel and d matrix your ghost knowing he's going to get attacked ne way. If its not a lot of overlords then just blind whats left of em and enjoy your nukage.