When filling out a job application the dignity of a homeless person is violated when they are forced to put a home address or a home phone number when they don't have either.
When being interviewed its very important to look as best as possible and being homeless they don't have the ability to shower to look the part for the job.
Being paid under the table hurts the immigrant family in that if that person gets caught the consequences will be far worse than if they were on a work visa.