Was the platform capable of recording cosmic rays other than gamma rays? If so, where is the data?
Yes, several experiments onboard the ISEE satellites were devoted to detecting or characterizing both solar and galactic cosmic rays, including, among others, the Low Energy Cosmic Ray Experiment (along with the Medium Energy Cosmic Ray Experiment and the High Energy Cosmic Ray Experiment) and the Heavy Isotope Spectrometer Telescope (a solid state detector).
Data (or results, if not raw data) from some of these experiments is certainly available online in the data archive you linked to (just searching for "cosmic ray" shortens the process), as well as a suite of other ISEE experiments and instruments. For instance, high-energy cosmic ray composition tables from ISEE-3 can be found here. Of course, not everything listed is available online; this set of low-energy ISEE-3 measurements is stored on microfilm.
NASA's mission definition of the International Sun Earth Explorer programm reads:
The International Sun-Earth Explorer, or ISEE, program was an international cooperative program between NASA and ESA designed to study the interaction of the solar wind with Earth’s magnetic system, the magnetosphere. The three ISEE spacecraft measured energetic particles, electric and magnetic fields, and plasma parameters.
In other words, the gamma ray observations indeed seem to be the most notable findings. As far as I can judge as layperson, the dataset cited in the question seems to be pretty complete. To be 100% sure, one would have to go to each an every publication, I fear.