They can spawn on any difficulty in groups of 3 and are a bit uncommon. They usually try to keep their distance from you and shoot you from afar. Their rifles also do not have lasers on them.
There is also a limit to how many Snipers can be present at once, although scripted Snipers seem to be unaffected by this.
Notes
This mod will only work if you are the host.
This mod may be incompatible with other mods that add and/or affect enemy spawngroups.
This mod is compatible with Streamlined Heisting, as screenshots were taken with it.