Is this the correct circuit for a Sourcing Digital Output
I've seen some examples including an additional transistor placed after the emitter of the opto, is this necessary?


It could be used as a buffer. Maybe the opto doesn't have enough current drive capability for the next stage, so an extra transistor with higher current rating can be added to your output.


  Also should the grounds on each side of the opto be different?


Usually, you use an opto to isolate two different circuits (high voltage 
vs low voltage) and prevent one from damaging/interfering with the other. But they can certainly be the same ground though.