I know you can use a playstation adapter with a wireless controller that way
But I just saw this on ebay I wonder how well it works!
If it weren't so expensive Id love to get one.

Dreamcast Wireless Controller * DreamConn * | eBay

VMU emulation. iI guess theres no real VMU interface but thats still pretty impressive I couldn't find any other information elsewhere.

He is also selling pre modded dreamcasts, and backlit VMUs. Including region free DEV bios boot, VGA, and Overclocked 240Mhz