Believe me, I've spent enough time with Play to know exactly how the build system does its thing with external dependencies.
The problem I'm referring to is that, for a long time at least (I know pre-2.1, maybe 2.1 as well), there was no way to aggregate non-Play projects--that is, ones that didn't have a conf directory and did have their own pom.xml or whatever--and use the recompiler. So if you were trying to build your project using an external Java/Scala domain object library that could be shared between projects and wanted it to hot-recompile while you're working (because I at least don't write every model class before I get going) you were in for a world of hurt.
The problem I'm referring to is that, for a long time at least (I know pre-2.1, maybe 2.1 as well), there was no way to aggregate non-Play projects--that is, ones that didn't have a conf directory and did have their own pom.xml or whatever--and use the recompiler. So if you were trying to build your project using an external Java/Scala domain object library that could be shared between projects and wanted it to hot-recompile while you're working (because I at least don't write every model class before I get going) you were in for a world of hurt.