Highly unlikely. States typically offer these incentives because the company they are wooing says they're going to bring x number of jobs to the area. So far VW is living up to that end of the bargain.
Said projections would have to be considerably lowered in the event of a unionized plant.
How so?
No, I'm not fond of government playing venture capitalists on behalf of the taxpayers, but if they do, they have the right to protect said investments.
And if VW closed its doors and left tomorrow, as unlikely as that may be, then what could Tennessee do about it?
Show me a UAW plant anywhere which is close to as productive as any reasonably run non-union plant by Toyota, Honda, Hyundai, etc. They aren't for a simple reason: the UAW (or any union of comparable militancy) bring in work rules which are inflexible and result in more people standing around and being paid to do nothing. If they are fortune, it might be just on occasion. If they aren't, it could be for years as GM discovered.
Of course, Tennessee could do NOTHING if VW closed its doors and left. Just as California could do nothing when Toyota shut down the NUMMI venture with General Motors/UAW.
Accordingly, anyone who thinks the state doesn't have a stake in management when they give incentives is as clueless as those who think venture capitalists won't try their hand at micromanagement the first time profits hint going south.