Assuming iPhoto supports your camera's version of RAW (there's no such thing as a "universal" RAW format), then yes and no.
iPhoto automatically makes a JPEG *copy* of the RAW photo, but the original RAW file is still stored -- it's just never touched. All the edits and such you do are to the JPEG copy.
There are alternatives photo managers/editors/etc for people that want to keep the RAW files more accessible to them (ahem). But bear in mind that RAW shouldn't be worked on directly -- one should always convert to TIFF or some other lossless (or lossy if you like) format before tweaking/editing/etc.