Is there anything wrong with keeping oil, salt, and vinegar together?
No, as you can keep them separately for a long time, The point is, no chemical reaction accur because they don't have right particles for a chemical reaction, it's just a mixture and no new substances is made. I think they are still healthy like that.

Also, accroding to a very nice article about keeping oil and vinager ( http://oilandvinegar.cruets.com/keeping-oil-and-vinegar ), despite they can be stored for a long period of time , depends on the place and container you keep them in:


  Olive oil and vinegar have four deadly enemies. They are:
  1. Age
  2. Heat
  3. Light
  4. Air 
  
  One of the above or a combination of any of these four can damage
  olive oil and vinegar beyond measure.


So in a dark and cool place and not a plastic container,they can be stored for 15 months.