One possibility is to compute the LocalStructure. Most of your atoms are probably still in FCC or BCC arrangements, while those around the vacancy are not. You can use this to color the atoms around the vacancy in the Viewer differently, and even hide those with crystalline local structure, and in this way you can "see" the vacancy.
Using a ghost atom is possible, but not if you are doing any optimization or molecular dynamics, as the ghost atom tends to move and sit on top of other atoms, i.e. it's not constrained to the vacancy site.