It's impossible to have a spawn that can't be camped. If you teleport in, they can camp the teleport destinations. If you have to go through a door that can only be opened on one side (a la TFC), they can camp that. The only thing that will stop spawn camping is the 1-2 second spawn invulnerability.
well, while these points are valid, I think having a separate spawn room would certainly help, I think moreso than 1 second of invincibility.
as it stands, 1 early focus skulk in a small game can take out the chair solo, running over to any spawning armor 0 marines, killing them, and resuming biting the chair. a couple seconds of invulnerability would just mean the skulk has to wait a couple seconds before he clicks his mouse to kill the marine. the marine would still stand next to no chance of killing a skulk that's already within biting distance. marines stand the best chance when a distance is put between them and their enemies.
that would be the advantage of another spawn room.
of course 1 or 2 could still guard the door or spawn room while 1 or 2 bite the chair, but this setup would still be advantageous for a couple reasons.
first, like I already hinted at, it would require more aliens to pull off a successful spawn camp.
secondly, it would draw sharper lines between spawncamping and simply killing the chair/hive. as it stands, saying 'no spawncamping in combat' is basically akin to saying 'no trying to win,' or 'don't kill people who are trying to kill you while you attack the goal.' if you started in a different room, it would be more obviously unethical to camp that room or the door outside that room, because you obviously wouldn't be trying to kill the hive/chair at the same time. it would actually make sense to say this practice is illegal.
third, the spawn rooms don't necessarily have to be anywhere near the hive/armory rooms... if it took marines 20 seconds to walk from their spawn to the chair, spawncamping would not only become unnecessary, but undesirable. it also might add more strategy to the game, as it would become wise to designate defenders and attackers... multiple entrances from the spawn room to the chair room would also make it impossible to camp them all.
fourth, a 1-way door would give a team a chance to let 2 or 3 ppl spawn before deciding to head out -- safety in numbers and all that...