I think he'd be an impact player for the Dawgs. At 6', 185 lbs. he's an inch taller and the same weight as UGA WRs Terry Godwin and Mecole Hardman, Jr. Fwiw, he's also faster (10.4 100m, 4.27 40-yd dash) than Godwin (4.6 40-yd dash) and Hardman (10.64 100m, 4.32 40-yd dash).
Robertson also made a "splash" at California as he started 13 of 14 games for the Bears, caught 57 passes for 837 yds (14.7 ypc) & 7 TDs, rushed 2x for 40 yds & 1 TD, and returned 10 kickoffs for 202 yds.
Fwiw, Bruce Feldman thinks Ole Miss (Jacob Peeler was Demetris' primary recruiter and WR Coach at California in 2016) and West Virginia (Jake Spavital was Demetris' offensive coordinator at California in 2016) are possible transfer destinations for Robertson.
Whether or not Demetris transfers to UGA may depend on his elder brother, Carlos, whom seems influential in his decision making.