No, the others are not. But it's difficult not to see it in Tau. It's not surprising that people are looking to Gundam models for Tau Conversions.
in the link you shared is one asking about Gundam conversions to stand in as Imperial nights.
The general bodyshape of the Tau battlesuits don't match most Gundams. Gundams tend to have large legs and a fairly slim top (barring some extra heavy ones or ones with wings or something). Tau battle suits follow the general WH40k shape--small legs, wider shoulders.
Color doesn't even close and of course the heads are way different.
Still makes no real sense to me.