Background check on greencard holders

I have someone that wants to rent a lot and they don’t have a SSN, they have a green card. The management company that has been doing my background checks says he has never ran into this and he can’t do it. That seems odd to me, but whatever.

So my question is what company are you using to run background checks on greencard holders or can’t it be done? I’m sure it gets sone every day, I just need to find out how.