I would say, "just try it".
Use gparted to squeeze down the W8 partition, add 2 or 3 partitions for ubuntu, install it and try it.
I am under the impression that you can't really tell until you use the BIOS on your computer with GRUB .
If you need a fallback, get a bootable rescue cd that can delete what you just put on and restore the master boot record.
If you have a problem, try to save your notes and post your notes and logs.