It should be fine. I suppose Ubuntu will take its own boot partition (or in this case the root partition) as its own. You can install Fedora GRUB on either the MBR or on Fedora's partition. To add new OS to GRUB list, it is easier with GRUB2 (On Ubuntu). You can just
so it would be easier to install Fedora's GRUB to the root partition. You can choose this option at install. However, if you plan on deleting Ubuntu later without reinstall Fedora, it would be easier to just replace Ubuntu's GRUB with Fedora's.