Yes you can still use JSP pages in Surf, as you have noted there is an example in one of the sample apps, also Alfresco Share uses a single JSP based site-index page. The JSPProcessor class still exists - that commented out code you can see has been refactored out and I will remove the detritus for the RC1 release.
You can retrieve the Surf RequestContext object thus:
The support for other model objects needs to be improved for JSP (and other languages such as Groovy), but you can retrieve a lot from the RequestContext.
RequestContext context = (RequestContext)request.getAttribute(RequestContext.ATTR_REQUEST_CONTEXT);