A Mathematical experiment was conducted to discern the emergence of time from entangled particles. I think it offers insight into the coexistence of omniscience, predeterminism, and free will.
Take for instance the Young's double slit experiment. A photon is shot, one at a time, towards two slits. It is impossible to tell which slit the photo passes through without collapsing the wave function with further measurement. (rough description google can explain more)
At some level there is a "choice" that occurs that is un-discernible through cause-effect mechanisms. Now ignore the word "choice" it's no one of cognitive behavior but a result randomly chosen between two binary states (left slit right slit) unencumbered by the environment.
It's suggested that in the "Toy Universe" Experiment that an observer entangled with the environment observing the photon would be left with a random occurrence.
But that to a "super-observer", an observer not quantumly entangled or part of the system would observe a series of temporal events that would appear determinable.
If an Omniscient being did exist, if they were not a part of this universe quantumly entangled with it. They could have an experience of time different from ours. But almost certainly experience the passage of our time differently. And view it as predetermined and known while.. we inside this temporal universe inside the same entangled mess, would discern choice as possible.
Ergo I think Omniscient Super-Observer and an free willed internal to this universe observer are, thanks to a kind of temporal relativity, not mutually exclusive.