You should be able to shoot lead bullets in a Glock, I'd just make sure they are hard and not pure lead. I shoot Oregon Trail bullets, they seem pretty hard and I have not noticed any leading in any of my guns.
Some people have postulated a relationship between the use of cast lead bullets and gun blowing up, arguing that buildup of lead in the chamber can lead to pressure buildups as well. The jury seems to be out on this one as a direct causation, but lead build-up will sometimes cause a round to not fully chamber, and as Glocks can discharge with the action not completely locked up ("out of battery," this can lead to a catastrophic failure.
Some suggestions to avoid having a gun fail on you are install a custom barrel (with a supported chamber), inspect your brass, load "hot loads" only in new brass, don't use range pickups, don't shoot "hot loads" from used brass and discard used brass sooner than you would normally.
Use calipers or case gauges to keep your reloads within spec. Check for excessive bulging in the case web and make sure your bullets are seated to the correct length. Also check for excessive case thinning or bulging.
There is a ton of info on the net about this subject. Glocks are frequently mentioned, probably because there are so many of them out there.
I am not an expert but I do think that Glock engineers are .I do not think they say no lead bullets just for the fun of it.Do you really want to get hurt or at least trash your gun just to save a little money on ammo.
Many shooters who like to shoot lead through their Glocks will buy an aftermarket barrel.
The factory standard, polygonal-rifled barrel can build-up with lead, causing a dangerous over-pressure condition.
I don't think the "No Lead" policy at Glock has anything to do with safety. Rather, I think it has to do with the type of rifling they use in their barrels. My Glock's rifling has a rounded look to it, and it does not provide enough grip on the lead bullets to get them to stabilize.
If you want to shoot lead bullets through a glock, buy an aftermarket barrel with conventional rifling.