I dunno. It depends on how you define, "emotional leader".
Smart is clearly one of the two 'fiery' emotional guys on the team (Morris being the other). The type of guys who let their temper be seen sometimes that is infectious and fires up others on the team. Righteous anger is a ferocious, powerful fuel.
But there are a lot of other emotions in the spectrum and I'm not sure Smart' really sets the emotional tone for this team more than I think a couple of others do.
I think Baynes and Rozier tend to be emotional sparks in a more 'positive energy' way that is, like Smart's, situational. The wear their positive energy on their sleeve and just as with Smart, they can be infectious, bringing others up with it.
But I think everyone one this team tends to follow Horford's lead on not just basketball (conducting the defense, funneling the offense) but also in the intense-but-positive-and-calm approach. In many ways, he's like Brad's on-court emotional surrogate. And all the other players seem to look up to him with such incredible respect.