I think you are making some very broad, sweeping generalizations about conservatives and republicans, and your question has a great deal of rancor and insults. Here goes my answer.
It is not just republicans who hire undocumented migrants—a lot of people do, and it is not particularly characteristic of conservatives or Republicans. Latinos generally do very good work and often for substandard wages, and people who can afford hired help often use them for that,
Conservatives and Republicans advocate a border wall so that we can control who comes into this country. They need to be vetted. We need to make sure they are not criminals or terrorists. Unfortunately the process takes more time than it ought to. But America welcomes immigrants—more than any other country in the world. We just want them to come in legally, whereas Democrats typically want open borders.
Many Republicans believe the infrastructure of the country (schools, clinics, government aid, etc etc) cannot support 100,000 or so new migrants per year, and many Republicans believe Democrats want the migrants for votes. They promise the migrants, the caravans, a lot if they come to America and claim asylum.
Others don’t want 100,000 or so new migrants because of competition for jobs in construction and agriculture. There are not enough jobs, migrants work for less, and because there aren’t enough jobs many will require aid from the government which also we can’t afford.
But the exploitation of migrants is not particularly what conservatives and republicans do, Some people, of any class, party, or description, will hire the cheap, high-quality labor of migrants from the south of our border.