Never heard of issues with the Luger frame. Parts in the toggle group, yes, they have been known to crack or break, but not the frame.
Many P08's were set up to fire the hotter 9mm used in sub machine guns of that day.
I've often heard this, or something like it, never once has anyone provided any proof, so I'm thinking its a BS rumor. The Germans were virtual fanatics about documenting everything, if there were anything done to the guns to "set them up for SMG ammo" there would be documentation.
Original Luger load was a 124gr @ 1050fps from a 4" (100mm) barrel.
Shortly before WWI this was changed to a 115gr @ 1150fps.
The toggle action is mechanically very efficient. It won't run well unless the ammo develops the recoil impulse it is made for. MV alone is not the whole story.
Up until the 1980s when we adopted the 9mm NATO as standard, US 9mm ammo could be, and was, whatever the maker felt like making, and US ammo makers had a long history of underloading metric calibers, compared to European loadings.
Lots of Lugers wouldn't run well, on US ammo. Since the fault "couldn't be" incompatibility with our ammo, the story became "they were made to shoot the hotter SMG ammo", and it stuck, and is still around today.
It's not true. If you run "SMG" ammo in your Luger, odds are high you will break it. If you run +P+ or +p ammo in your Luger, odds are something will fail, and fairly soon.
Now, having said that, someone will come along and relate how they've run thousands of rounds of hot SMG stuff through their Luger with no issues. And, maybe they have, but that doesn't mean YOUR Luger will handle the same thing the same way.
Shoot an all matching # gun and break a numbered part, and you no longer have an all matching # gun. Could turn a $2500 gun into a $1200 gun with a single pull of the trigger.
Do remember that the last German Military Lugers were made in 1942. The "newest" ones are currently 78 years old this year. Most are older.
There are some Lugers that were made in the 70s, and later, Mauser did a run of "Swiss pattern" guns and some others have produced small numbers of Lugers since then, as commercial guns. But mass production of military Lugers ended during WWII.
Shoot 115gr @ 1150fps, its what they were made for. Shoot anything else and you're rolling the dice.