Single-Atom Catalysts (SACs) have emerged as a new class of materials with the best noble metal utilization. The atomic dispersion leads to strong coupling with the support, which can enable facile electron transfer between both. In the present work, we evaluate how the reducibility of the oxide matrix, in this case, ceria, affects the dynamic charge transfer for isolated gold and platinum atoms. We find that the number of accessible states in the electronic ensembles increases significantly due to oxide defects, converting them into almost continuous distributions that can expand up to 1 eV in magnitude. At elevated temperatures, surface reduction slows down electron transfer events involving the single-atom, thus stabilizing unusual platinum charge states. Our results demonstrate how the coupling of the electronic structure of the support and single-atom redox states can be harvested to control the dynamic behavior of SACs.