Does it complain if you mount the whole device (on Linux that would be /dev/sda rather than /dev/sda1 or whatever)? Because perhaps the problem is that there's enough of a partition table data structure there to convince MacOS to look for one, but it's not valid, as the camera formatted the whole device without partitioning it.

If you can't even mount /dev/sda, then the first thing I'd do (being a Linux weenie but not a Mac weenie, but I imagine similar facilities are available) is dd the whole device into a file on a PC, and try and mount that over loopback (on Linux that skips all the partition-checking code). If that doesn't work either, then dd /dev/zero over the first few sectors of the device, format it (in the camera again) as FAT, then create a new file whose first sector comes from the newly-formatted card and all of whose subsequent sectors come from the original dump. That new file should be mountable over loopback unless the filesystem is totally hosed.

Peter