We have a legacy monitoring product that is deployed on WLS as well.
If we can embed it into EM console frame as a portalet, our Manager server will be reserved so that we can save our development effort.
My question is that does EM GC support portal technology or does EM team have a plan to support it?
The Enterprise Manager Extensibility Kit (EDK) does not provide support for directly embedding portlets, so the answer is no. However, the EDK (doc located here http://docs.oracle.com/cd/E24628_01/doc.121/e25159/toc.htm) as well as metric extensions (located here http://docs.oracle.com/cd/E24628_01/doc.121/e24473/metric_extension.htm#autoId0) do allow you to pull information from a wide variety of sources, which may get you what you need. I hope that helps.