Hooray! I've baked a cheesecake which didn't crack as it cooled. I used the cheesecake mixture from this Gordon Ramsay recipe, although I made my own biscuit crumb base from 150g crushed HobNob biscuits and 60g unsalted butter, which I chilled instead of baking.
As you can see from the photo, there wasn't much swirling of the chocolate - 75g of melted chocolate almost covered the surface, and however much I tried I couldn't get it to swirl into the cheesecake mixture - it stayed stubbornly on the surface. It might have been better to mix the chocolate with some of the cheesecake mixture, but that would probably alter the texture of the cheesecake, which I wouldn't want to do. Perhaps the chocolate was still too warm and liquid - if it was cooler and thicker it might not have spread so far, and allowed a more swirly effect to be achieved.