No… According to the Annotated Dragonlance Chronicles Tracy Hickman put the difference as being :
“Fizban is a crazed wizard owned by TSR under copyright, while Zifnab is a completely different crazed wizard owned by Margaret and I. Incidentally, neither Fizban or Zifnab have any relationship to Zanfib – a crazed wizard from our Starshield series.”
So yeah, he’s the same character but they couldn’t use Fizban in their other books as they didn’t know the copyright.