You can call it "fake" trading (i.e. buying and selling something, pay just the fee for the trade and create artificial volume).
Or in the case of zero fee exchanges (not Poloniex according to their posted fee rates, but who knows what private discounts/rebates may exist), you don't even have to pay the fee to do it.
I'm not sure about that. A lot of people are following Ethereum, and I believe that the volume is genuine. If I was part of the Poloniex exchange, I would not risk my reputation like that. They have become a leading (not only altcoin) exchange in the world and they are making a lot of money anyways.
I'm not sure what you're disagreeing with. There are certainly other exchanges in the crypto space that charge zero fees, meaning if wash trading does occur (LOL if anyone doubts it), the people doing it don't even need to pay the fees in order to create fake volume.
In terms of Polo, I don't know if they offer any discounts or rebates privately beyond what they give everyone, but it is not unusual, or even improper, to give incentive discounts or rebates to high volume market makers. I've been offered this in the past by other crypto exchanges (not Polo).
I agree with you that the original premise of Polo being in on the wash trading is unlikely, but I wasn't suggesting that at all.