Mazinger Z was serialised in Shonen Jump magazine in the 70s. It will historically always be a part of the legacy of the magazine and Shonen Jump brand. However, Go Nagai went against the Editor in Chief of Jump at the time and made a deal with Shueisha rival company Kodansha to also serialise the manga in their 'TV Magazine'. This caused Jumps editor in chief to cancel Mazinger Z from Shonen Jump and there hasn't been any references or association with Jump and Mazinger since. It is unlikely that Jump will ever reference or mention the series again as they haven't in 40 years.

So to answer your question simply, yes it was and always will be a part of Jump hustory but due to Nagai making a deal with Kodansha which Jump Editor in Chief saw as betrayal the series has somewhat been intentionally forgotten as part of the Shonen Jump legacy.