Gilliam was described as a safety in discussions with Stoops, I believe.
Correct, the UK Coaches (plural) have already said that Gilliam will be a safety and/or a nickel.
With the exception of JD Harmon (this year), Westry, Baity, Robinson & Griffin are currently projected to be the 2 deep CB's for the next 3 years, if things hold. Kendall Randolph, who has 2 years left, can also slide over from Nickel & Dime to play corner, when needed.
With the exception of Marcus McWilson (this year), Edwards, West, Walker & Gilliam are currently projected to be the 2 deep @ safety for the next 3 years, if things hold. Gilliam (and Edwards) can also play nickel. So Gilliam probably will have to move to nickel, if Cole plays safety.
At nickel & dime, Blake McClain has 1 year left & Kendall Randolph has 2 left. UK also has youngsters, J Tucker, K Beckham & W Jackson. Again, Gilliam may have to play here, initially, rather than Safety.
These are just the guys that should be on campus this fall. These names don't include any 2017 or 2018 recruits. Once those guys arrive, DB might become a real log jam. The good news is that all can RS & the depth will be insane.
All that said, UK might appear to be pretty loaded @ WR, but they might be even more loaded @ DB, IMHO.