Strictly speaking for American contractors, I'm 99% sure that is not true. If you have any contract with the government for space stuff, all of your workers have to be citizens. I'm not even sure they'd let a permanent resident work there because of ITAR.
Permanent residents are considered US persons under ITAR, so provided the company's activities are limited to civilian space projects it isn't an issue. However, if the company has defense contracts and requires employees to obtain a security clearance, that requires citizenship.