You can do animation in SFM because it's an animation program. Taunts are only available in the game once Valve puts them in.
Things like taunt items create a temporary animation entity ("instanced_scripted_scene") which can force animations to fire on target objects.But you can still add custom prop_dynamic animations to hammer. Sure, you can't add a player animation to use on player\engineer, but you can animate a custom player compatible with hammer. Think of the animated tanks from frontline, but people instead. I don't know how it's done but I know that it's possible.