I don't have a Heiland SplitGrade System, but the manual indicates that you can read densities because the controller has a density mode (Dichtemessung).
In that mode you would put a negative in your enlarger and look for the area that is the most clear, take a measurement, then take other measurements to find their density difference from the first reading.
Using it as a densitometer this way will include flare, which will affect the "highest" density readings (like readings above 2.0 density).
This won't hurt your ability to read the thin parts of the negative around 0.10 density, which is where you will look when you are trying to find film speeds.
So it looks like you will be able to use the system as a densitometer.