No! Mixed-species vivariums are pretty much best left to very experienced herpers only, and require extensive research, lots of set-up, and a very diligent keeper. Even if you find compatible species, it is quite difficult to set the habitats up so that they are not stressed by the presence of the other species. Also, your sav and rat snake are not only quite incompatible species (the snake would not stand a chance due to size and monitor's appetites, although rats will eat lizards too if they are small enough), but their habitat needs are different enough that you really couldn't house them together without sacrificing the needs of at least one. They also probably both carry parasite and bacteria that are normal to them but alien to the other animal.