Yes if you are careful. However, you will probably have to break a warranty sticker like on the Muvo. Then it may not be returnable.
Your best bet on ebay is to ask the seller if it has been tested on a pda. That's what I did, and the seller told me it worked on his ipaq and camera. Also, ask if the microdrive has firmware 3.04 listed on the back, as I have heard those don't work in Axims. Mine has no firmware version listed at all. There are no guarantees that it will work though, so I bought a Muvo that had the md replaced with a 256mb cf card. In the event that the card didn't work, I would at least be able to use it in the Muvo and have an extra 256mb cf card.
Since the ST1 ended up working fine, I gave the mp3 player to my mom.
I found this on Google. It may be helpful if you plan to get the rio.