While this has nothing to do with global illumination, yes, other plugins that do post-effects or modify the render pipeline are unlikely to be compatible. The only reason Eosin's plugin works is because that is based on SuperShot, which knows about PostMagic and handles things accordingly.
ColorGrading can be done via the UserLUT module, although not very conveniently. Take a screenshot of your scene, load it into Photoshop, GIMP or whatever external software you like. Apply your ColorGrading, Brightness, Saturation or similar effects there. Take note of the exact values and order you apply them. Then load the neutral LUT texture and apply exactly the same effects in the same order, save as a new LUT texture. Then use that with the UserLUT module. Only limitation is that it can only do color mapping, it can't do anything that depends on neighboring pixels, like blur, DoF, etc.
PostMagic is a plugin that makes hidden VaM features available. It does not implement these effects itself, just offers the UI and makes some render pipeline modifications so already available (but hidden) effects can be enabled. Therefore it is not possible to add effects or fix issues with them (e.g. those black or white color blobs reported frequently, caused by bad geometry).
To improve or add effects, someone would have to implement these effects from scratch, which is a LOT of work and requires a lot of knowledge to do well. Off-the-shelve stuff usually won't work, due to copyright, but also due to being designed to be added via UnityEditor, not as a VaM plugin. There is
Post Processing by
@moyashi which does this, for example. But AFAIK it does neither support SuperShot nor Eosin's plugin.
