Forget what I said, you were correct about needing in Compile. I finally figured out my issue. I was using these lines outside of .settings(), like this:
unmanagedResourceDirectories in Compile += file("/etc/config")
val main = play.Project(appName, appVersion, appDependencies).settings(resolvers ++= Seq(...))
This doesn't cause a compile error, and intellij recognized the unmanagedResourceDirectories variable. When I initially tried placing that code inside the same .settings() as the resolvers, it threw an error. The correct way seems to be to provide the configuration with its own .settings() block, like this:
val main = play.Project(appName, appVersion, appDependencies).settings(resolvers ++= Seq(...)).settings(unmanagedResourceDirectories in Compile += file("/etc/config"))
Thanks for the help.