I am sorry, You DID say Overwatch but I am so accustomed to everyone using Epoch or Overpoch now that I totally glossed over that.
The vehicles for Overwatch are spawned in by the database and require the correct hiveext.dll file to write to the database.
If you are using the default Overwatch files but are not using the default overwatch database schema .. perhaps its not writing the new locations to the database. there have been other issues as well often after installing Base building. What about other objects such as tents or the hidden stash? do those spawn in the correct location after restarts?
We cant tell from your arma2oaserver.rpt file because it ends before anyone has even joined the server so there is no valuable information there. So run the server long enough to get some good information. You might also want to disable SargeAI since its spamming the server with errors that will make it hard to see any other actual errors.