Note that MgT2 has apparently misspelled the name: according to T5, they are the Essaray, not Esseray. And I am not saying this simply to nit-pick, but I believe it is important in order to interpret who they are supposed to be.
As noted, on the T5.00 CD (p. 417) there is the IISS "Secret Map" from the time of the IISS Second Survey (ca 1065), which noted the "Essaray", along with a number of other populated regions about the galaxy with accompanying "redacted" text. On the original T5 CD, there is an earlier version of this map that labelled this area "SRAL". "Essaray" is fairly clearly a "spelled out" version of "S-R-A-L" (the "L" having been dropped in the final version).
So what is SRA(L)? I have pored over the redacted parts of the Secret Second Survey text for quite sometime after T5's publication, and have been able to reconstruct about 35% of it with a fairly high degree of confidence level. I did this by looking closely at those parts of the letters that rise above and fall below the strike-thru, and logically deducing from the grammar and logic flow of the sentence (and a bit of intuition) what certain words most likely were, which often in turn suggested further words surrounding those that fit the parts of letters in accompanying text.
My reading of the part about the Essaray and the Barren Arm is as follows ("recovered" text is in bold italics):
ESSARAY: Explorers have seen evidence of Self-Replicating _________________________________ worlds and sending missions to ____________ ________ Level 29 Threat.
THE BARREN ARM: For reasons which are unclear, the occurrence of intelligent life on worlds of the Scotum Crux Arm is at least an order of magnitude lower than in other Arms.
S = Self R = Replicating A = Artificial (?) / Android (?) L = (Life) (?)
I did all of this prior to the publication of AotI. The information we get from MgT2 Starter Set about the Esseray [sic] merely serves to confirm it for me.
The Essaray are the "androids" in AotI that were constructing the vessel on Dathsuts/Vland 1703.
Note the footnote in Dathsuts Chapter in the just published Annotated PDF version of AotI on p. 130:
SRA or Essaray. The secret archives hold reports of vast swaths of star systems whose worlds have been strip-mined for resources for projects such as we see here. There are also entire world surfaces populated by robots such as these.
