Support is a build style, not a role. If you take 0 cs, build gp10 and wards, you're a support. Regardless of which champ you pick. In that sense, support is not viable on TT. That doesn't mean that champs that traditionally play support are not viable.

I did 4 games as Taric, it was not very successful. He has nothing that hits hard in team fights.

Nunu, Lulu, Leona, all are viable when built support-y

HoG
Aegis
Frozen Heart
etc etc

lol no one has even mentioned alistair. I play alistair in 80% of my 3's games as a tanky ap. Works great.