I'll answer some of your questions about EJB embeddable API support in GF.
1. It requires a preinstalled instance to use it as a configuration reference only (e.g. you'd preconfigure resources there). I've seen people working off this limitation by adding domain.xml to the classpath and (may be) adding some properties to createEJBContainer() call.
2. It constructs the deployment artifact from the entries in the classpath, so if there is only 1 ejb module, it'll be deployed as-is (directory or jar). If there are more than one such module, a temp EAR will be created by constructing a directory structure copying and unpacking modules according to GF exploded directory rules.
3. There are bugs that prevent support for libraries in addition to the ejb module (e.g. if you package your JPA artifacts separately), in case of a single ejb module for any type of the library, and in case of multiple ejb modules, for JPA libraries only.
4. There are known problems with security support, and MDBs, and WebServices are not yet supported.
HTH,
-marina
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