Polish immigrants and Mexicans are different?

Your Polish son in law is probably not willing to stay here illegally.

That having been said, many Polish and other eastern Europeans ARE here illegally, trust me I see many of them daily working around here in the Chicago area (especially north side). The illegal ones are not doing civil engineering degree work however, they are doing work such as housekeeping, sometimes truck driving nowadays, and sometimes manual work in factories.

Since your son in law wants a white-collar type of position in an office presumably (civil engineering) , he likely will not be in that category and will not be willing to do something like simply stay here past when his visa expires and work somewhere where a Polish boss will pay him cash, or obtain a fake SS #, or otherwise trick the system.

The people in the gated community are probably 90% illegal aliens. Those folks don't really follow the rules, or the laws.

Countries bring immigrants to do jobs that cannot be filled. The Mexicans probably willing to do jobs people with degrees will not do. There are people in your own country getting degree in civil engineering they would get the jobs first but how many want to pick vegetables in a hot field?