No, it’s purposefully disabled because it’s not possible with MPlayer to FF some types of streams over HTTP.

I think ff/rew are quite useful with web streams. In my custom build, I re-enabled this feature commenting out few lines of source code.

The only problem is that almost always wiimc hangs for few seconds, in particular when moving forward. I wonder if it is not possible (or how much it costs in terms of development) to run the stream filling task in a separate thread, leaving wiimc alive.