I can't give you a definitive answer, but here's my understanding:
When you partition a hard disk drive or SSD, you create physical volumes. Two physical volumes (maybe any number, I haven't checked) can be combined to make a logical volume. That's what a Fusion Drive is. I don't think you can partition a logical volume (i.e., a Fusion Drive).
So, at least in my understanding, you could partition your HDD into two physical volumes, then combine them with the SSD physical volume into a single logical volume (aka Fusion Drive). But the Fusion drive shows up as a single filesystem volume -- you would have no control over where your game (for example) was located among those three partitions because there's just one filesystem per volume (logical, in this case). So there's no point in making the extra HDD partition. However, the game would get to take advantage of the Fusion Drive's SSD speed.
Instead, you could combine only one of the HDD partitions with the SSD to make a Fusion Drive, and leave the other HDD partition as it's own volume (with its own filesystem). Now you could put the game on the second HDD partition, but it will never get the benefit of the SSD since the SSD is part of the Fusion Drive's (logical) volume, only.
My advice is to use a single Fusion Drive and enjoy it. The appropriate file blocks from all your commonly used apps and games will live on the SSD, and you won't have to manage a thing yourself. Splitting your storage into OS X and "data" partitions wastes space because you can never know the exact size the OS partition should be (and it's a real inconvenience if it's made it too small so it's usually made too large). It also defeats the "smarts" of the Fusion Drive, because now some frequently-used data resides on a different volume and is ineligible to be moved to the SSD.
The only advantage I can think of where having two smaller partitions is better than one large one is if you want to use a disk cloning utility to clone the partitions to external drive(s) that are too small to accept a clone of a single larger partition. Even that doesn't convince me because I believe one could software-raid the externals together to make a single larger volume to accept the clone image...
Well, guess I got a little wordy... sorry! Good luck
Brian.
