As long as it sees the card at all, it will create a device node which you can dd from. If the card is so damaged that it no longer actually appears to be a flash card at all, you may be out of luck.

Edit: I expect that this is the case with MacOSX, too, but I don't know that for sure and I don't know where that device node might show up. You might check dmesg after you insert it to see if it says anything