The two cartridges are almost the same, dimensionally. People may quibble about them being interchangable, but I would not worry about it in guns of good condition. Much harder to find .30 Mauser ammo than it is 7.62x25.
It was the most powerful common pistol round in existence until the .357 Magnum showed up, as I recall. It was highly regarded in its time. The PPsH submachinegun of the Soviets in WWII (The Great Patriot War) did significant execution.
Mauser also made broomhandles in 9x25 export caliber.That caliber is close to .357 mag. in performance.
***Much harder to find .30 Mauser ammo than it is 7.62x25. ***
I believe the ATF tried to ban this ammo as “armor piercing”.