I was forced to read ALL of the books you mentioned and it was a VERY painful episode in my education.The teacher was MAD for dos Passos;damned near genuflected every time she said his name.YUCK!
Not a commie - the Reds always sickened him, even though he rubbed shoulders with them as a Leftie. I'm sorry your teacher made you read USA - I happen to like those books but can understand why they'd stick in your throat, especially if you were forced to read them. You ought to read "Adventures of a Young Man" if he want to see how he viewed the Marxist crowd in later years (later? - it was published in 1939).
To me USA was mostly opposed to the collusion between banks, big business, big government, and jingoistic big media. I imagine most workers today, union and non-union, enjoy many benefits that were unheard of when company goons were killing strikers in coal country and outside auto plants. Those are the times he was writing his early stuff in.
I don't believe that Orwell was ever a strident commie. He made the distinction between socialism and communism. He was always an avid socialist...but he was a rabid anti-Stalinist.