The base power would be 1 if it was done on Showdown!, but I have a hard time believing the exact same thing happens in the cartridge games.
Apparently, the answer was on Smogon all along. The fact that I was the first to find this suggests that I'm the only person who uses both Pokebase and Smogon Forums. Is this true? Anyway,
When hacked into normal move slots, damaging Z-moves (Hydro Vortex, Bloom Doom, etc) becomes 1 BP / -- Accuracy moves of their respective types. Special Z-moves (Catastropika, pulverizing Pancake, etc) function normally with their actual Base Powers and effects. All normal move slot Z-Moves have 1 PP ( PP Ups don't work). You can use as many normal move slot Z-Moves as you want in a battle. You cannot power up a normal slot Z-Move with a Z-Crystal (it won't recognize the move as that typing at all). (UltiMario) Their PP can be restored with a Leppa Berry. (UltiMario)
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