There are 3 tracks; Leadership, Specialist and Teaching. So ST and LT, at least semantically speaking, are not in Leadership track.

They are however expected to lead in mentoring, pedagogy, etc. They are also called Teacher Leaders.

So depends on how you look at it, STs, LTs and MTs can be considered leaders, or not.
It also depends on the school. Some treat them as leaders, some don't, and some treat them as those who couldn't make it on Leadership track. It really depends.