Galkas galk'in. All I see.

Dancer wouldn't be a useful job in a supporting role even if they fixed Waltzes because the situations where it used to be useful are pretty much gone. Where would we heal?
Abyssea - It is either already possible or there is little SE could do to promote it.
Voidwatch - It is pretty much impossible due to AoEs.
Walk of Echoes - See Voidwatch.
Legion - See Voidwatch.
Neo-NI - Not really playing a supporting role here if you are either off solo or have a real healer.
Old content - Isn't really done with more than 3 people.

The only situation I can think of that would promote a supporting-DNC role is meleeburning DC Dynamis monsters for R/Ex pop items.