Yes it is possible to get a big grouper out of a hole. I have found that with grouper you rarely get a kill shot on the first one. The first thing they will do is make a line to their cave/hole/overhang etc. and try to get in as deep as possible.
This is normal for grouper hunting. I always try to tightline my fish and try to keep them from going too deep under water. If they get holed up in a cave in under 30 ft you have a much better chance of getting them. Dont waste your time with a small gun hunting grouper you will just loose your gear or injure fish
I have never shot a grouper that was just sitting in a hole or cave. All of the grouper that I have shot have been 1-2ft over the rocks(bottom) on patrol of their territory. The "hole" is where they run in 1.5sec after you shoot them to try to hide.
When they hole up it is best to go up and take some good calming breaths. Getting them out of the hole can be work and will tire you out very fast. Do not try to push it getting them out, it is better to make several short dives and slowly work him out.
Dive down with your knife out and try to get a hand in the cave and brain him. if that dosent work try to grab some gills and pull, if that dosent work a simple stab might get him bleeding real good. Then its a waiting game. A good knife is key when hunting grouper. The spear line us usualy the problem and is usualy wrapped up in the rocks in the cave or hole.
the longest time it took me to get a grouper out of a hole was almost an hour. I needed help from my buddy. beware of getting tangled in your rigging.
Be aware of other animals in the area that are attracted to the noise and blood of a grouper kill. The grouper will kick wildly in its hole after shot and its like a dinner bell going off under water.
Best to try to tight line them after shot and prevent a hole up.
I hunt mainly grouper down here in Baja. there are 4 different types, and they all taste great!!
GTB
www.gonetobaja.com