Just spewing out my thoughts, wouldn't the Gashathi be considered the Forerunners or even Precursors by the Covenant? Technically speaking the backstory of the Gashathi is the same as the theirs, being the oldest living beigns in the galaxy (I guess I kinda missed that backstory, but can you blame me for not copying that one part from a 60k NS at 1AM?) who were also almost destroyed by something very similar to the Flood. And between you and me, I did take some merit of inspiration from them.

I'd be happy to collab with them, since both of our races are looking for the long abandoned technology of their ancestors.