Heroes of Might & Magic III: Horn of the Abyss

yes. originally, the Tank was an alternative to the Yeti; now, only one Yeti remains.

Correct. Artillery units are acceptable for Heroes of Might and Magic III, but tanks and other technology should be avoided (it diminishes the fantasy setting).
Also, another question: will the "new" creatures from Warlords of the West (Werewolves, Nightmares, etc.) remain? ... Or rather, will they be included in the expansion?