Zam Wesell is extremely fast, and you could probably get up to about 270 speed with good speed mods (up to 285 with GREAT mods) which should outspeed most Vaders. She has two abilities that give AoE debuffs.
However, this increases speed, not turn meter. So even if you are able to land the DoTs it's likely that Vader goes next, lands his DoTs, throws the saber, then the entire enemy team goes (even with your improved speed). This is all assuming you don't have an enemy Sion that allows Nihilus to go as well as someone else mentioned...
You may actually be better off running GK in the fifth slot and just trying to tank your way through the fight until Boba can land some nasty Executes.
