I don't think there is any ambiguity.
If you try selling live corals, it is likely that the listings will be reported and removed.
Live corals are animals, you probably know already that they are classified as invertebrates, and are not allowed on Ebay.
Sellers who already have live corals listed may not be UK based or they may simply be flouting the rules and getting away with it.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)