Are you really using a separate engine for this, or is the pump of the existing system driven by a PTO on the truck's engine or transmission? I assumed that snow blowers with their own engines used on loaders and airport runway clearing equipment usually drive the blower directly from the engine, not via hydraulics.
Neither hydraulic pumps and motors nor electric generators and motors are perfectly efficient. If the electric stuff is more efficient than the hydraulic stuff, less engine power would be needed; if the electric stuff is less efficient than the hydraulic stuff, more engine power would be needed.
The idea of an electric drive without a battery is the same as a diesel-electric locomotive or most diesel-electric or turbine-electric ships. The details depend on design choices (such as AC versus DC generators and motors), but regardless of the details the power output is the power input minus the power lost to inefficiency.
Yes, a traditional 50 kW engine and generator set is huge, because it uses century-old technology.