Emoticons are limited to bitmap fonts because the sprites come from the same atlas as the font's characters. This is what makes it possible to have only one draw call. Dynamic fonts use a separate texture for their character glyphs, so there would need to be two or more separate draw calls / buffer sets per label. Each NGUI widget can only be associated with one material -- just how it was all designed.
The only way to get what emoticons in the dynamic fonts would be to somehow insert sprites as glyphs into the dynamic font itself.
