Not really - I've sampled a lot of silage from drought corn. Even at 40 bu/acre corn, the silage has at least 80% of the energy of regular silage - this is due to nutrients in the stalks that never got into the grain. The big difference is tonnage - since half of the weight as fed is from the grain (and most of the weight on a dry matter basis) the lack of corn directly reduces the amount of tons you will chop.