the market fell 3% in may but volatility didn't go anywhere near this high. If individual stocks can be manipulated, why can't futures. It's kinda weird to have vix suddenly rally 5% intraday when the market is flat or even rising slightly.
It sounds to me you don't understand VIX nor volatility...
If Vols are vey low, they may well go up while the market rallies... because a big move up is still volatile. VIX is not just a fear gage, it actually represents future expected volatility... also up.
Also, VIX is calculated from the options IV's... which are a bit harder to manipulate then just bidding up futures.
If there's risks ahead (brexit, interest rate hike, Trump for Pres, Japan financing difficulties, South China Sea issues...uncertainty in general), skew in options will rise and therefore VIX as well, even if the market stays flat.
There is no linear relationship between VIX and ES.... while you can use it as a hedge, just must make assumptions on which move in VIX should correspond with ES... like a sudden 3% drop might have bigger impact then a slow 5% slide... or vice versa.
It depends on whether the market expects something to happen.
For instance, after the London bombings the markets closed higher and IV lower...