I'm having a hard time figuring out how I would go about disabling all Vanilla mobs only? This include Passive, or Hostile. Is there a catch all for disabling Vanilla mobs that would work instead of having to list every single Vanilla mob ID?

Mob Filters for example has a minecraft:* wild card that can be used to just block Vanilla mobs.

This is simply so that mobs from other mods can still spawn normally - but for the use case, on Neo Forge, this is the only mod for mob controlling that is updated, so I wanted to learn how to do that here. Just can't seem to find anything in the documentation.

if memory serves you can use this to deny it.

"mod":"minecraft", "incontrol":false

I'd use the incontrol flag for this, so you can use spawning rules for vanilla mobs and prevent normal spawning.