Do I just have to make sure they have the same data-dir?
With 0.11 (and possibly 0.10.3.1, though I'm not 100% certain this was ready then), there is no particular precautions to take in order to share a database between two daemons. Pointing the daemons to the same directory using
--data-dir should be safe. I'm not sure this has been tested a lot, however, so if anything like corruption should happen, please report it to https://github.com/monero-project/issues.