normal people have displayed the ability to survive on space hulks. quite simply an ork can't survive without air. therefore they cannot survive without an atmosphere.
The SpaceHulks is a mass of starships wrecks and other spaces waste. The oxygen system of some starships can still work, so the orks spores can grow. And idem the atmosphere system. And if the SpaceHulks don t have any oxygen and atmosphere, why is there often Genestealers?
"Genestealers are stronger and hardier than Humans, able to withstand even the most hostile environments unprotected, including hard vacuum, and are capable of living for centuries" http://wh40k.lexicanum.com/wiki/Genestealer For your information, a vaccum is basically space, no oxygen, no atmosphere. However, logic dictates that large objects such as a Space Hulk, have a weak gravity field. Thus, they can support an atmosphere. It even says on the wiki, to my surprise: "They drift in and out of the warp through space and during the millennia the lost ships join together into one enormous body. Many times they are so huge that they have their own atmosphere and gravity." http://wh40k.lexicanum.com/wiki/Space_Hulk
Remember though Aadil it's many times not every time. Point being Orks are extremely resilient and have shown at times the ability to survive and even prosper in enviroments other organisms would struggle to imagine surviving in. Hell we're talking about a species who if their body is badly damaged can behead themselves; then stitch their head to a nearby "healfy" body and get back up to continue fighting.
An Ork is several times more resilient than a Space Marine. The things Orks are able to survive is ridiculous then again you're talking about a Race bred to fight Necrons and C'Tan
Orks aren't resistant to genestealers, the problem for nids though is that infested orks act way too odd for Orks and wind up getting killed to stop making the other boyz feel da heeby jeebeez. Orks are also not more resilient than Space Marines. That's only if they grow big enough to be nobs. Fresh outta the 'shroom orks are stronger than normal humans but don't stand a chance against Space Marines. Remember the wise words of Mista Nailbrain "Marinez boss. Dey don't kome much 'arder den dat." Also Orks cannot survive in a vacum. But Orks know that, so they take precautions. Remember Orky tech. All they need is a paper bag with a tube to a science-y looking tank and you have an Orky rebreather, and that's enough to keep Orks goin.
Depends if said Space Marine is wearing power armor/terminator armor. Because that armor really is what makes the difference in battles. It's able to deflect most bullets, and take hard hits most of the time, plus it enhances an Astartes strength. But if a fresh Scout Marine were to take on a fresh ork out of the 'shroom, most likely the ork would win.
