I'm not official, but unless the wording on Overwhelm is an exception, I'm going to say definitely not. Like attacks, you declare targets and then the action is carried out based on those targets.
Much better stated than what I said. Thanks!
to completely rez a months old post, she can be immune to them, but she can't hit you if she can't get behind you =] We had an un-cast match at worlds where Ra and turret bot were making our position very uninviting, but Tachyon couldn't use Hypersonic assault to hit us, as we were stacked to the back edge of the map.
I'm also of the persuasion that she's best countered by ignoring her, as if you've survived her initial assault, you've generally rendered her inept until you want to make her your team's third point. Otherwise she's giving your team two points, if she incaps herself on purpose. Sometimes potent, yes, but dice are a fickle mistress.