I was actually basing it on the size of the "System Volume Information" folder. When I first set up the ram disk a few days ago, that folder got to 280 meg. But now it's at zero bytes, even after a few hours of uptime. So, it's definitely not indexing. Sorry for the bother.
I noticed that the drives created by AIM have the "Allow files on this drive to have contents indexed..." option selected by default on their Properties page. Can an option be added to the RamDisk Configuration window to disable indexing by default? I know I can disable indexing by checking the "Removable media" checkbox, but that has other effects, like more aggressive cache-flushing, which I don't want.