The way it works is like this:
Android is installed to ${partition}/android-..../. This is basically a data folder, a system folder or .sfs (squashed file system) file, kernel, and ramdisks.
You only need to install GRUB if you're going to give over your MBR. Otherwise just configure whatever bootloader you're using.
My system uses GRUB2 in first disk and chainloads Android-x86's GRUB because I lazy.