Questions.

Eh, IMHO, it's seems like it's loosely based on the Kikaider stuff. More of a Gaiden or re-imagining of it. It's set the setting sorta of flips their roles with Hadaider being the good guy and the Kikaider being the bad guy. I think the city protector angel guy is Kikaider but i don't think they call him that but it's been a little bit since i sat down and watched it. I had it on VHS.. I think i remember seeing a special edition DVD somewhere i've been wanting to pick up

I know it's approximately six years after you asked these questions and you'll never see this, but I just rewatched the movie today so here are your answers in reverse order. Spoilers ahead, to the nth degree.

The Hakaider in this movie is a different person than presumably any of the five that appeared in either of the original Tokusatsu series. Gurjev, the villain of the piece, claims to have created Hakaider long before the events of the movie but that could easily mean that he popped a new brain into an old Hakaider he found laying around. Flick isn't super clear on that point.

Kikaider is another story. Throughout the movie, Gurjev is served by a silver and white robot called Michael. Michael is a ruthless second in command and nearly destroys Hakaider when they finally fight. The Mechanical Violator wins, only for Michael to be reborn as a giant tank-like thing...with Kikaider's face on it.

You can interpret this information two ways: either both Kikaider shows happened and Gurjev bent first Hakaider and then Kikaider to his will once the world ended, or this is a complete alternate reality. Personally, I kind of like the former but my biggest exposure to Kikaider so far has been the REBOOT version's two episode arc on Kamen Rider Gaim.