Is chlorine dioxide (ClO2) some kind of bleach?

No. While chlorine dioxide has chlorine in its name, its chemistry is very different from the corrosive chemistry of chlorine bleach. The primary differences are that chlorine dioxide is non-caustic, safer, and gentler than bleach. Further, chlorine bleach produces harmful fumes and by-products to the environment, including trihalomethanes (THM) and haloacetic acids (HAAS). Vital Oxide breaks down to a simple salt, producing no harmful by-products.