Is there any way to know what pre-processing a particular camera might be doing to its sensor data?
You can assume that most manufacturers apply some Secret Sauce® to their raw and JPEGs - that means that if you don't want to do extra work just skip to the end.
Searching for an answer led me to the dcraw website where it says: "... use dcraw.c as the documentation that camera makers refuse to provide" and goes on to say that if your camera isn't amongst the several hundred supported ones "... I need a photo of a Wolf Faust, ColorChecker, CMP, or other calibrated color chart.".
Those links are an interesting read but the last leads to CMP's webpage: Raw RGB levels and their interpretation, which recommends RawDigger.
RawDigger is also mentioned on our site here: https://photo.stackexchange.com/a/50715/37074 , in a question about accessing pure raw data. RawDigger has a "Profile Edition" which claims is useful for: "Advance Study of Sensor and Lens - creating of sensor calibration data, linearization data, or device data for color profiling, including Flat Field normalization" and can create ICC Color Profiles. It has a fully functional 30-day trial.
So with some test charts and a 'raw file analyzer' you can test your camera and with expertise know what pre-processing is being done in-camera.
For Astrophotography, and to avoid the need to analyze a camera not designed for extreme accuracy, you might consider an Astrophotography Camera such as the Atik 414EX cooled CCD camera (designed to eliminate noise, and not use any secret-sauce) or something more user friendly like the Canon EOS 60Da or Nikon D810a with a specialized IR cut filter and no optical low-pass filter.
Why wreck the light before it hits your sensor and then worry about pre-processing of the raw data?
Use this link to search for more info about pre-processing raw camera Astrophotography.