The Church is under no obligation to check the citizenship of people who attend Mass. But it would be wrong to hire any of them. And it would be wrong to help them disobey or evade the law.
I understand their sympathy. But this is just wrong.
I’m Catholic, I withheld money from the “Bishop’s Annual Appeal” for this reason. I would back them up against most government intrusion, not this. I hate to say this, but I think they’re motivated more by tithing then anything else.