It will help you overclock your RAM a little higher, but if you need a heatsink to achieve those results, it means you're pushing your RAM too far anyway. Since this is highly dependent on the ambient temperature, your RAM will overheat accordingly if the temperature goes up by a few degrees. Unless you have active cooling on RAM, I wouldn't just use heatsinks to do heavier overclocking.
It would of course be a good idea to use those heatsinks "just in case".. It will probably void the warranty because you will have to remove those little stickers from your memory that say "4GB PC2100, Corsair"..