Best way to transfer a few tables from reserve server to production
I think linked server and MERGE would be the best way to do it.  Set it to run at the appropriate interval and go for it.  Take care with the merge statement so that it properly detects when to do an update or not.  But since they are on the same subnet, it should perform adequately.  

But linked servers have their own share of risks as well, make sure you set them up correctly (pass through security, etc.).  

If you already have SSIS configured in your environment, that may be the more manageable approach.