Honestly I always thought they spawn close to the objective then run in. I heard about people saying they spawn within but have never seen it myself.
https://www.halowaypoint.com/en-us/games/halo-5-guardians/xbox-one/game-clips?page=1&gamertag=noexqss#ugc_halo-5-guardians_xbox-one_gameclip_noexqss_1cdfe368-a570-4e6a-8e73-563df17dda4d
Skirmish at Darkstar
Round 1: Defend the East Armory
(Run from drop off point to the other side of the map)
Round 2: Defend the West Armory
(Run to the other side)
…We didn’t make it to round 3
I Can confirm that they spawn in the armory.
A few days ago I was in the armory with a scattershot (5 “bullets” remaining) and then 10 crawlers, 2 soldiers and 2 knights spawned INSIDE the armory. I was like “F***” and I died…