Although I have not tested with a pre-installed Windows 8 OS, this should work fine as Gparted is compatible with GPT disks. You could also try shrinking the partition in Windows 8 if it will let you shrink it small enough to fit on the SSD. I can confirm this process works with my own Windows 8.1 installation on a GPT disk, so I'd expect this to also work with a pre-installed Windows 8.1 installation.
The ddrescue step works regardless of what's on the hard disk, including Mac OS, third party bootloaders, etc, so long as the last partition ends within the outer boundary of the SSD. So if you're cloning to a 240GB, I recommend ending the last partition at least within 10% of the outer boundary before the clone, e.g. 200GB for a 240GB to 256GB SSD. You can then expand the partition to fill the drive once the SSD is installed.
The only issue you may have is if there is a recovery (or other) partition located at the end of the hard disk. In this video, I showed how to do keep such a partition on the original hard disk, but delete its reference from the resulting clone using fdisk. However, fdisk is not compatible with GPT. From what I read, gdisk works just like fdisk and supports GPT, but I have not tested this technique with a GPT disk. I'll give it a try when I get time.