Don't most exchange accounts fall under this category of account trading that is banned?
For the most part, Yes.
I am mostly referring to exchanges that require full KYC before depositing or trading like Coinbase, Kraken, Binance etc. If a member here is buying or selling 5–10 accounts of such a service, then they are definitely going against their ToS and probably using stolen identities for KYC or selling hacked accounts.
You have pretty much a good idea about these casinos and their terms of operation (which explains why you said everything above)... It's impossible for them to formulate just anything and get an approval from the casinos, what does that tell you? It's either they buy these fake identities from the dark web and manipulate with it or, those are hacked accounts.
Should such posts be reported too, even when not listed yet?
Don't wait for a validation. Always do what's right in the least possible chances that you have.