So I decided to copy that icon to my camera's memory card instead. When I used the icon from the memory card, the custom icon now "sticks," even after ejecting the card. I created a folder on the root of the memory card called ICON, and applied the custom icon to that folder, but anywhere on the root should be fine and the icon will not be deleted when originals are deleted within iPhoto.
Now, when I plug in my digital camera, I am greeted with a nice icon of my Coolpix, instead of that bland white one. Hope this helps others who are trying to achieve the same result. If you need help setting custom icons, this tutorial at xicons will help.

