Is it safe to allow users to import their old blogs?

I am almost ready to launch my multisite, which will be open to the public to create users and sites. I would like to allow users to import their old blogs using the standard import tools, but I'm concerned about security. My question is, would site admins be able to import malicious code via the import tools? I'm hoping the import tool would only import posts, comments and images, and filter out any code.