They were both pretty hated minorities. So how was the relationship between them? Did they also hate each other or did they try to cooperate?
Can you explain what you mean by "Early USA"?
A lot of the discussion of the parallels between black slaves and Irish indentured servants centers on people who came over in the 17th century, well before the USA was founded. Most of the descendants of today's Irish Americans actually arrived in the middle 19th century and beyond, which can't really be considered the early USA either.