Theoretically they should just work...
Theoretically.
But we're talking Apple here. They have their own way of doing things and the same thing applies to the raw dng files. Apple has their own idea on how those should work which means iphoto is a bit difficult with more than a few dng files.
The advantage of dng should have been that it's an open, simple standard that should work everywhere... But Apple, as usual with these things, doesn't completely like open standards at all, so they have a few of their own implementations.
Anyway you should be able to use the import feature. If that doesn't work however...