Dry firing a Glock will not hurt it. It's a good thing, too, because dry firing practice would be a royal pain if one needed snap caps--you can't just cock the hammer back but have to cycle the slide.
Actually, you do NOT have to cycle the slide, you just need to chamber check your gun. Moving the slide about 1/2 inch will reset the trigger. You are NOT cocking it like a 1911.
You have to dry fire the things to get them back in the tupperware. If it were not good for the gun, I would think they'd come up with a different storage container.
Also, the more you pull a GLock trigger, the smoother it gets. Get to it!