Yes hybrid vehicles can significantly reduce greenhouse emissions as they have been proven to significantly use less fuel that the usual gas based car due to the ability to use electricity. A hybrid car such as the Honda Civic Hybrid can go 44 miles per gallon while the conventional gas using car can only travel 32 miles per gallon, and will less fuel usage there will be less greenhouse emissions produced by the car.
Hybrid vehicles have already been shown that they contribute to helping go green. One of the ways it does this is by using less fossil fuels and keeping from adding more to the pollution. If everyone was able to afford a hybrid vehicle I believe we would see a very big difference in greenhouse emissions.