Ok, so to break down what we can;
For starters; I know more about Halo CE then H2V. H2V seems to use Squad Groups, Squads and Zones in place of Encounters, Squads and Platoons. I assume they're analogs, so here's a quick description if you're unfamiliar, and you'll have to translate or transform to H2V yourself.
- Squads - AI placement. Has Spawn Points, and the AI type determined by entire squad or individual spawn. Has selections for which firing position index it uses
- Encounter - Parent container for squads. Has the team index for all children squad and firing positions locations. Maybe an elite, grunt and jackal squad exist in an encounter for each section of the map.
- Platoon - Optional group container for squads. Exists as a child of an encounter. Multiple squads of an encounter can be grouped into a platoon and acted upon at once in scripts. For example, perhaps multiple waves of covenant attack. You can track each wave individually if they were assigned a different platoon
Hopefully H2V didn't change too much and the Zones/Squads/Squad Groups are basically the above.
The AI will not spawn because as you said there's no script making them. Unticking "Not Initially Placed" will cause them to be created at level start, but they may very well kill one another or wander off before you get next to them.
Normally AI are created by the command (ai_place <encounter_name>). To my knowledge, which is fairly limited, there is no tool for editing or extracting existing map scripts for H2V.
If your tool allows it, you can try duplicating the cut squads into an earlier scenario, or if that fails incorporate them into a pre-existing squad. If Bungie was lazy, they may have only used;
If so, by duplicating the squad you're trying to spawn and placing it as part of that encounter, then when that encounter is placed by the scripts so is yours. However, there's an alternate version of that command;
and if that version is used, then you're SOL as it references a specific squad and not the encounter as a whole. If that's the case, you'd have to re-create your spawn points and placements inside an existing squad, so that when it creates the stock content it also places yours. This is acceptable, but the prior example is preferable as you're now editing the counts of AI which is often the foundation of the game's scripts. You may end up softlocking the game by placing yourself in a situation you can't advance (I.E (door_locked_until ai=0) and you have A.I. behind the door.)
I mean maybe. I don't know. Maybe none of this works.