This is a common concern. The PPSSPP emulator itself is completely legal. The cheat database file contains only text strings (codes) that modify RAM values in a game. It does not contain ROMs, BIOS files, or copyrighted game code.
No. Cheats only modify real-time RAM. They do not overclock hardware or write permanent viruses. However, a badly written cheat can freeze your emulator. Simply force-close PPSSPP. ppsspp cheats db file download