I had a similar problem with Killzone 3 save data. When I activated my new machine (under account management on the ps3 xmb) it solved the problem. That game save unlocker works too, I can confirm that gt5 definately works using that method. Its a bit weird when you copy it over. After unlocking I copied it to my ps3, the file appeared in my ps3 game save data but included none of my unlocks.
When I started the game it loaded in with everything intact. After quiting tthe game I looked at the file again on my xmb and it included all the unlocks. Maybe the game itself fills in some blanks that the game save unlocker cant quite achieve.
The post earlier about the gt5 update that lets you copy the file only seems to let you copy to usb, it still wouldnt load for me when the game loaded up. It may be due to some id issues on my old machine. I was copying from a cfw system to an ofw system.