Hi Leonardo,
It is not possible to use the just the "UI" component of any editor. The good work completed by Plugtree allows the editors to be embedded in a IFRAME within "your application" but the editor still communicates with Guvnor's back-end for persistence etc; all you do is provide a container for the UI. The client-side of the editors are furthermore coupled with GWT-RPC and hence not easily separated. There are plans (well, talks at the moment) to implement a pluggable (so you can add new editors to Guvnor) and re-usable (so you can re-use Guvnor's editors) architecture for the editors but the necessary re-design and re-implementation is not about to happen any day soon.
With kind regards,
Mike