I went to the local labor emporium and got some Brazilians who did it
for $7.00/hr. I didn't even ask - I just said to the guy at the
employment desk I needed four people, explained what I wanted and
there they were.

Now, when I have to get the hay off the field or some other task like
stacking wood for the winter, I just make the call and presto, more
people to help at the state minimum which I believe now is $7.25.

You're (presumably) hiring legal workers and paying a legal wage. No problemo.
Casual, manual, short term jobs don't require great social sensitivity to fill-
but the hiring practices shouldn't be predatory or illegal and yours would not
seem to be.