All add-ons only work on a game released in the same region.
In this case, the free add-ons from Japan will only work with the Japanese version of GT6.
To be a little more detailed:
All games are coded with a unique product ID. The same game will have different product IDs in different regions. A game can only recognize and use add-ons that have the same product ID. An exception to this are sequels to games that can use add-ons from previous versions, such as LittleBigPlanet and the Rock Band/Guitar Hero games.
Ratchet & Clank: Into the Nexus is certainly more scaled down than Crack in Time, It is kinda halfway between a full fledged game and one of those standalone DLCs like Infamous: Festival of Blood and Far Cry: Blood Dragon. Great pick-up for $15-20 (especially if you don't have Quest for Booty), but the original $40 asking price was definitely pushing it.
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