It depends on how the implementation is made. A basic implementation like 1 server for dB + X server for file hosting just need FTP access and nothing more, the machines can run complete different OS or even HTTP servers, you want them only for storage so you don't need PHP or other dynamic language. Since you want to serve static content you may want to set a nginx or lighttpd server.

But a more complex thing like a balanced setup need more things in common. Honestly, a killer custom multi-server setup is way too expensive but the basic implementation is cheap.

You can find real life architectures on http://highscalability.com/ and get an idea.