The litres of fuel consumed per hundred kilometers are similar between say, the Camry and the Jetta TDI (2009) -- and this is partly due to the fact that diesel has more energy per litre than gasoline. (See wikipedia for a good explanation, if this isn't obvious.) However, the clean diesel has far lower emissions that gasoline hybrid engines in nearly every category, except CO2 -- CO2 tonnes over the life cycle of the vehicle is still expected to be somewhat higher than the hybrid gas. However, in my mind the effects of high amounts of CO are often much more directly felt than CO2.
I recently built emissions models for both those vehicles, the results unfortunately on my hard drive at work, not here at my finger tips.
Given the low emissions of a modern clean diesel engine, the motivation to go with a hybrid isn't at all clear.
