The only way you can make your tablet useful for osu! is to make it work like an input device for your PC i.e. make it work like a graphics tablet. There are plenty of apps that can do that, the most popular being
RemoteDroid (do not expect stellar performance though).
There is no way to install osu! on your Galaxy Tab. You can install
osu!droid but it's just a clone, not the actual game.