In general, “robber barons” like these three men accepted immigrants and disliked unions. They accepted immigrants in part because of their dislike for unions.
The owners of big corporations in those days did not like labor unions. They felt that the unions were organizations that would hurt their businesses by unreasonably driving up wages. They also did not like the idea of having to share power over their business empires.
Their dislike of unions was a major driver of their attitudes towards immigrants. They might not have liked everything about the immigrants, but they did like the fact that there were so many of them who would work in factories for low wages and without joining unions. This allowed the “robber barons” to use immigrant workers, or the threat of them, to break the unions.