Not just when the plates are put down but also when the bar is sitting loaded between sets. But its mostly when the weights are put down.
The stress on the bar is higher from the Olympic lifts even though you do them with less weight. Prior to the invention of bumper plates, barbells bending and/or breaking during Olympic weightlifting competitions was common. And platforms tended to get damaged too. That's *why* the bumper plates were invented. The earliest ones tended to break a lot but at least the barbells and platforms were intact. Now bumper plates have gotten so good that they tend to last a lifetime. A quality barbell and a good set of bumpers should now outlast the owner. That wasn't always the case!
Even on a four inch thick wooden lifting platform a failed snatch or jerk with any type of iron plates is a recipe for damaging something. You can lower a power clean safely (Google's for Mark's video "The Iron Problem") using iron plates but you shouldn't drop it.
When bumpers land unevenly (as they are apt to do when dropped from a height), there is some elasticity to the collision. It's been too long since I did physics for me to comment any further.
You can add some iron to a barbell loaded with bumpers (the change plates all tend to be iron and smaller diameter). But 1x45 bumper + 3x45 bumpers per side is not something I would do to a barbell I liked.
In strongman they have pulling wheels that raise the height of the bar and then they add iron outside of it. But I'm not even sure they use barbells that have bearings. I've never done strongman. For those purposes you could use an axle (no bearing) barbell.
If you live somewhere that houses are built without basements (like here in Florida) you had better be extra careful about this stuff. What breaks easier than a barbell? Plumbing that's right underneath a concrete slab and the repair is a big job!
You can't fit more than about 500lbs of cost-effective training bumpers on a barbell. Competition bumpers ($$$$$) you will get much more at a huge cost. So that's another factor to consider if expecting to deadlift very far north of 500.
I know of no barbell nor bumper plate manufacturer that would honor the warranty if a single 45lb bumper per side were mixed with multiple 45lb iron plates.