Sure it is. My dad lived here for 60 years. He was a legal green card holder, served in the military, but never became a citizen. He worked and contributed the entire time.
I apologize I’m not familiar with it but a 10 fold increase in the program suggests something sinister
I never knew noncitizens could be given SS numbers. Now, I’m wondering whether our ancestors ever became citizens themselves when they came here in the early 1900s.