Does the G5 use the same RAW format as the G1?

The format is probably similar in that it will be an rw2 file (ie a Panasonic raw file), but the specifics will be different for each camera. Most raw processing software, including Apple's, is regularly updated to support new cameras and the G5 is certainly supported by the major ones. Whether your version of iPhoto supports it or not I don't know, but if it is reasonably recent you should be able to download an update to your Mac if this hasn't already been done.