Interesting to see the responses.
What I've been instructed (by LEO and former LEO who largely operate the range where I've taken classes) is that Glocks and pretty much all modern pistols have some form of internal safeties that block the strikers/firing pins from moving fully forward unless the trigger is depressed. Hence, that round in the chamber cannot be fired so long as the trigger remains in the holster.
The usual concern I've heard expressed is that striker guns' triggers are lighter than DA triggers and therefore much easier to accidentally depress if a finger goes where it shouldn't when drawing or holstering. I can appreciate that aspect. "Training, training, training" is essential, but anyone can make a thoughtless error when startled or under attack.
I've also heard the counterargument that if someone is startled enough to grab a handful of gun, the difference between a 6 lb trigger and a 12 lb trigger isn't going to stop anyone from squeezing a trigger.
At any rate, the few LEO I've talked to there certainly teach that it's safe to carry chambered rounds. In my case, it's a rare day that my carry pistol (either a Springfield XD or a Walther PPS--both of which are basically Glock-like designs) ever leaves its holster outside of a range. Goes into the safe in its holster, comes out of its safe in its holster. Taking apart for cleaning is the only exception, and even then I'm taking it out of its holster after the holster is off the belt and the whole rig is aimed in a safe direction.
(Oh--I have met one person--and I do mean one--who is a fan of manual safeties on guns, ONLY for the purpose of taking the gun in/out of a holster or handling it when you do not want it to be able to fire. I can see his point...safety on...into holster...carry with safety off...taking out to clean, etc, safety on....and so forth. The majority of striker guns don't usually seem to have external safeties. I do kind of like the safety that's on the new Springfield XDE, since it's unobtrusive but easy to operate intentionally, and you can load/unload with the safety on. For whatever peace of mind that may afford).