Can't comment directly on the ST, but mil-spec generators generally are separately excited, mainly so that they will start with a a load across the output which would normally prevent the voltage build-up from residual magnetism in the machine.
Feeding from a battery is OK, or a well-smoothed DC fed from the output, but do bear in mind that the field windings can only dissipate a certain amount of heat, and it can be very easy to overdrive the field, especially at low rpm and high loadings on the output.
It's not difficult to produce a regulator, there are plenty of other discussions on here about that, but making it controllable and resistant to spikes etc is another matter, and takes some thought.
I think GE published some details in one of their thyristor app notes in the 1970's, when Markon and Stamford went into solid-state stuff in a big way.
Peter