There are at least 2 problems:
resource_pool.erl:25: Polymorphic opaque types not supported yet
There was a discussion on the first point recently on the mailing and bugs list. I don't agree with how dialyzer does it.
@rvirding did that discussion ended up to something? Dialyzer is a great tool, but there are 2 things that killed all my attempts to verify somewhat large project: the one that is mentioned in this issue and the fact that Dialyzer can't handle polymorphic opaque types.