I solved it!
Ever wonder? during the campaign menu when you idle and that trailer like video plays and it shows the second mission and once you get the warthog from E419 it comes with 2 armored marines?
However in the final game you only get one marine in the turret?
Well… I decided to consult with the PC. I used sapien for CE and loaded up that level…
Near the transition to that tunnel above on the hill that is out of bounds during game play you can find the warthog and marine spawn.
AND GUESS WHAT?! Now we know why only 1 marine spawns!!
The second marine is a tad bit to high and when he spawns he falls to his death before the warthog and the other marine teleports to the pelican!!
I assume Bungie never fixed this bug or did this in purpose so we take another marine from that life boat crash with us…