I mean, I believe the Glock requires you to pull the trigger before you disassemble it. Guess you better have a snap cap then.
You don't need a snap cap to disassemble a Glock without damage.
Once or twice shouldn't be an issue but repeatedly it's a statistical issue.
You can definitely dryfire a Glock more than "once or twice" without damage.
There's dryfiring and there's dryfiring.
If, when you say "dryfiring" you mean that you're going to dryfire to disassemble the gun, to perform basic function checks, and for occasional practice then there's no problem with dryfiring without snapcaps as long as the manufacturer of the firearm doesn't forbid dryfiring.
BUT, if, when you say "dryfiring" you mean that you're going to dryfire every night while you watch TV and keep it up, day after day, until the skin of your finger wears the face of the trigger to a mirror smooth finish, then it would probably be wise for you to use snapcaps--and probably other precautions against wear/damage.
Known problem with Glocks.
Well, yes and no.
Yes, it is possible, if you really try hard, to eventually damage a Glock by dryfiring it.
No, I don't think it's entirely accurate to call it a "problem with Glocks". I think you can wear out just about anything if you try hard enough. I've got a Ruger P89 that actually has serious wear to the frame from a LOT of dryfiring. The trigger pivots against the frame and that friction, over time, has actually caused enough wear that the trigger linkage tolerances have been altered to the point that the gun won't fire consistently in double-action.