It depends on how you use it. (i.e. how much force you apply)
But my personal assessment is (and correct me if i'm wrong)
there's the rubber tip type styli --> shouldn't be a problem
there's the metal mesh type styli --> no idea, might have abrasive effect if a lot of force is applied. Glass isn't that easily scratched though. it's not exactly a knife point.
there's the plastic disc type styli --> shouldn't be a problem
there's the metal disc type styli --> no idea. again, applying too much force at the wrong angle may have an abrasive effect
this will probably differ when applied to a protective screen cover as that has no where near the hardness of glass of course.
M.