So if I download a redump iso that is almost 8GB and I burn it on a dual layer disc and if the game is on the xbox 360 backwards compatible, should I be able to play it on my xbox 360?
Sure, if you really want/"need" the highest quality there is you can grab remuxes. But will be pretty big file sizes, so disks can be better in that regard.
But piracy is free so...
some bluray rips are kinda crappy, remuxes are a more safe bet, but i usually don't have trouble finding a good rip, there are certain groups to avoid and some to look out for