While rare, malicious actors have historically embedded exploits within save files. The PS Vita's PSP emulator contains a blacklist of known exploited games. The PSDevWiki notes that the PSP emulator on Vita blocks specific savegame exploits that were used in the past to run custom code on the PSP.
If you play Tekken 3 as a PS1 Classic digital bubble or through the Adrenaline PSP homebrew environment, the Vita uses the virtual memory card format ( .VMP ). tekken 3 all characters unlocked save file psv hot