Many UEFI machines still come with legacy Windows installation.
Are you sure about that? It is often not obvious to boot in UEFI mode, at least with the new AMI BIOS. The BIOS will switch automatically but it defaults to Legacy. If you boot a medium, such as Ubuntu live CD or openSUSE DVD (not CD!), which includes the two kinds of setup, it will start the MBR setup, unless you call the BIOS setup (once the DVD is inserted) and explicitely set the boot priority to the UEFI medium.
This is weird. We should have a look at your menu.lst.
Yes, it works. You’ll just have to run update-grub after a kernel update.
- but as soon as you can boot openSUSE, it wouldn’t hurt to install its Grub in its root partition.