Boris Spider, Fel Orcs don't appear in the game, but if you suggesting elite Horde members then I'll leave those Fel Orcs in to be edited.
Oh and by the way, Lothar, Khadgar, and Garona will be featured in the campaign, but Garona will have only a little cameo and the beginning, and the Azeroth Defenders flee the land from the Horde.
Well in the Prologue or Demo Campaign, this will happen and then the fun happens during the Second War with the main campaigns themselves.