Hahahaha! You're really hilarious. Asking a spirit of the dead and use itself as a suicide bomber is still considered natural, eh? When did school of nature have access to buff dissipation and does even remove mana from enemies? So a DH is also using nature as well when they create or spawn soul fragments and command it to attack their target as soul/spirit bomb?
Are you sure you are playing World of Warcraft and it is Warcraft's lore you are talking about?!
So Malfurion is not using the dead because in WC3 he is your hero unit and you as a player has control of your basic worker "dead disembodied spirit of fellow Night Elves" to control them to farm for gold, gather wood, repair their buildings and safrifice themselves to become ancients natural...