Nope. The first G4s were released in 1999, OSX beta came out in Sept 2000 (OSX server came out in 1999, though). The first few generations of G4 shipped with OS9, including the Yikes! and the Sawtooth; I bought mine in mid 2000 and it came with 9.2.
EDIT: the "nope" was in reference to them shipping with OSX. Any G4 can run OSX up to Tiger, and will likely be able to run Leopard slowwwwwly. You can upgrade the processors of most G4s to above 1gHz, which will meet the minimum requirements for Leopard.