You are missing a piece of the puzzle, read under "Highly synchronous" here: http://www.playframework.com/documentation/2.2.x/ThreadPools
So, yes, you would want it to be non-blocking but if you cannot have that because of JPA/JDBC etc. then you can configure play like you would with the regular Java web containers - a thread pool with lots of threads. It won't give you all that play can give but it might very well be good enough for you.
You could also create a specific thread pool/execution context and run the JPA/JDBC stuff only on that and keep the rest of your server non blocking.