Short answer- yes with a 'but'...
Long answer- Roadmap maps based upon U.S. Census Bureau Tiger Data are Public Domain. Some of the other files (i.e.- non-U.S.) available at http://roadmap.sourceforge.net/maps.html include information from the DCW some of which is Copyright by ESRI. And the DCW shapefiles are Copyright Stephen Woodbridge. But they are labeled as such...

[Disclaimer time- While I am the maintainer of the Roadmap for Maemo project, it is a fork. I am not associated with the fine folks at the main sourceforge project. Due to OS2008 requirements, mainly DBUS, the changes I've made to the codebase aren't really upstreamable. So Roadmap for Maemo is and is likely to remain a separate project.]

Also, while we're talking map formats, openstreetmaps.org support is coming! (Roadmap already supports the maps, but the buildmap_osm tool is only in CVS right now. I'm looking at building a static binary for linux to offer for download on the garage page.) But if you're running linux and you're impatient, you can checkout Roadmap from CVS and start build maps on the PC to transfer to your tablet now!

Cheers,
kernelpanic