Well from my understanding, if the Derelict campaign history is adopted into 'official' FS2 HLP 'history', then it means that all those Sathanas' weren't built, but BORN.
And if that intertwines with Infero, it would mean that the 'Gargant' is their mothership
After all it did receive the classification 'SM Gargant'. (Shivan Mothership).
I reckon is probably the most probable theory. It would be much quicker for shivans to some how have some giant , living, breathing ship giving 'birth' to these warships, then using materials to construct them. Given the arachnid-like appearance of the ships, i think my theory is at least plausable.