Dreamcast doesn't have flash nor compatibility with any modern browser based games. Only about six games are online for Dreamcast right now and 100 Swords was never released outside of Japan, and it's not online anymore.
Bomberman is not online. PSO is.
Bomberman was online for a long period of time, and people from the west could play on those servers, that supported it.
Even if a dreamcast game is not released outside of Japan, should not stop a person from playing the game itself. If PSO can be reloaded, then all of these other games should be able to.
Flash does not need a browser to run, it can be ran from DOS. Newer flash types are resources hogs, depending on which version of X script, is used. The Dreamcast should be able to run something equal or great then that, to be able to run a web browser. It is not a Sega Saturn for crying out loud.
I know many people are, and have been playing the online games for years. I am just wondering if your talking about a unique product, or usage for the Dreamcast.