Manageability has to do with how easy to monitor your running application and change its configuration. An ORM certainly provides features that can help improve it so yes it has got a positive impact especially for for the configuration side of thing.
Maintainability has to do with how easy to fix bugs in an application without impacting other functionalities. This has more to do with the design/architecture of your system. You can use all the bleeding edge frameworks you want in your system and still have a crappy maintainability. So the ORM in itself doesnt really have a significant impact on maintainability, be it positive or negative.
That's my view.
SCJP 5 , SCWCD 5, SCEA 5
subject: How the usage of an ORM impacts manageability and maintainability