They have to be Spartan-II because they are also too old to be Spartan-III's. Bungie really should've put more effort into making Halo Reach fit in with canon.
Covenant plasma weapons (plasma rifle, plasma pistol, etc) do more damage to shields and less damage to health. Projectile weapons (Carbine, Needle Rifle, BR, etc.) do equal damage to health and shields.
They don't need to enter the spawn since in SWAT nobody has shields. If they added one-way shields to block to the spawns, one team would just end up hiding behind the shields because the other team would kill them immediately if they left.
No offense, but that's the most ridiculous thing that I've ever heard. Why should I have to sit through the rest of the match, which well only consist of me getting killed quickly and repeatedly, when the rest of my team decided that it would be fine to quit before the game is even halfway over? I shouldn't. Sitting through the rest of the match doesn't make me a "stronger player", it just makes me a complete idiot.