His eye helps Rashid to see though those who who cross the Gates..
page 338 Cold Days After Harry exclaims that his job is so secret that his eye needs a disguise.
"But they need a good eye here to be sure that the things that must remain outside do not slip in unnoticed.
"Inside the wounded," I guessed. "Or returning troops. Or medics."
Rashid is then pleased that Harry is learning.. But it isn't just his eye either..
On 339 Harry asks him how he knows that someone is infested and Rashid answers;
"Experience," he said. "Decades of it. The Sight can help, but. . ."
Rashid hesitated. I recognized it instantly, the hiccup in one's thoughts when one stumbled
over a truly hideous memory gained with the Sight, like I had with the--- Ugh. ---the naagloshii.
Rashid then goes on to say it is an art not a skill... Then he says something rather interesting
Time, or a bit of questionable attention from the Fates and a ridiculously enormous tool." He tapped a finger against his false eye.
Notice he says, " attention from the Fates
and" He doesn't exactly say he also got his false eye from them, which is implied, but also implied is he got some teaching or other skills from the Fates, not just his eye.. It also implies that normally the Fates do not interfere with free will much like Heaven.