I don't know of any slicing software producing G2/G3, Marlin will interpret it.
The issue is identifying curve segments in the model, since STL is the commonly used input format and curves have already been converted to line segments during export.
In fact you could write a post processor that was just as effective at identifying curves as the slicing software can be.
Most CAM software works around this by using something other than STL for interchange.
