No, VGA won't be able to drive the display to its maximum resolution. If the monitor requires dual-DVI then it's capable of higher than HD. The only other connector capable of the same resolutions as dual-DVI is Displayport.
Yes, the thunderbolt port on a mac can be used as a mini-displayport connector (some earlier Macs are only mini-displayport, not thunderbolt, but the connector is the same).
VGA is your last option. DVI is better, and will run HD. Dual-DVI or DP are the options you need. A cheaper monitor without DP will require the expensive connector. Might be worth considering swapping the monitor.