Hi Tony,
I’m not sure I understand your question. Measuring the instrumental and atmospheric response for a symbiotic is no different to any other star in that you want to use a reference star close in altitude and azimuth to the target and for which you have a good spectrum, so ideally a Miles library star but failing that a Pickles spectrum for the same spectral type as the reference star. It doesn’t need to have a spectral type similar to your target star. That should enable you to correct your measured spectrum to the exo-atmospheric spectrum of the target, whatever type of star it is.
Apologies if I’ve misunderstood what you were asking. If so, try again!
David