If you are uneasy about not being able to prove you took the file then I suggest you convert to DNG before submitting. It makes the files more accessible to buyers and you still have the native RAW to 'prove' ownership.
I have RAW files online for many of my images and sell about 1 RAW for every 20 images sold. I have had about 5 requests from buyers to upload RAW images that I didn't have online. My personal take on the advantage of RAW files is that people may select the 'only vector/RAW' option in searches even if they don't buy the RAW (just in case they want to later), giving you more search visibility. posted in How many designers need and buy RAW format?
As far as I know you get the $0.20 upload bonus for images already on line, but you do not get the exclusive image bonus for prior sales.
In terms of online files, if you search in the database and then search again with 'exclusive' checked you'll find that only about 5-7% of images in a given search are exclusive on DT. posted in How many are Exclusive Member