Currently there are two versions of ProB available for Rodin.
The first one is based on the old Java API and supports Rodin 2.8 and Rodin 3.x. The update site comes built in into Rodin, see Tutorial_Rodin_First_Step.
The second, still experimental, one is based on the new ProB Java API (aka ProB 2.0).
Details about nightly releases of both versions are available on the Download page.
Because the UI components provided by the ProB Java API are based on web technologies, we were able create a simple plugin for the Rodin 3 tool that provides the user with all of the functionality of ProB within Rodin. The plugin uses views with embedded Eclipse SWT browsers to access the user interface components that are shipped with the ProB Java API library.