I like checking myself and this is a common question asked by clients. A small hole is the drywall is an easy repair and the piece of mind it offers many is priceless. Plumbers are tougher and trust their skills. We do not have their years of cofiendence to draw on so an inspection is not over the top.
With a large diamond coring drill bit you can pre drill a scrap of tile or plastic. Then place this around the small hole. Use the pre0-dilled piece to hold the drill bit in location and drill a larger hole. You can then give yourself a little room to look. Make sure the trim of the shower arm covers the hole.
These drill bits are a good $40-$60.00. Using a larger hole when cutting the tile in the first place can avoid this tough check. We have been waterproofing these shower arm wing backs to leak outside the shower tile's assembly. Pretty slick what you can do with off cuts of membrane and some random PVC fittings.