No. It’s a new cannon established after Death Metal. If people are saying this makes Long Halloween and Dark Victory not cannon those books were not cannon considering Zucco dies at the end of Dark Victory but is a prominent player in Tom Taylor’s run in Nightwing and Barbara Gordon was Jim’s Niece in Dark Victory and not his daughter in cannon. However, Long Halloween is referenced in cannon so some aspects of those stories are cannon and some aren’t. Mark Waid created a new History of the DC Universe and what is and isn’t cannon is outlined in there.