I have used CA over Teak Oil and it worked fine. I soaked the call in the Teak oil per the directions on the can and hung to dry for 24hrs or more. Light sand (400 grit) the barrel outside, wipe of the dust and apply the CA.
If you have a problem on oily woods give the barrel a coat of sanding sealer (shellac) and after that dries you should be able to follow with any finish you wish.
Fred