One would have to add in the blog_id though. I know most folks place their bbpress in a subdirectory under their site. The problem with that is that with any blog, going to the bbpress subdirectory (ie username.mymu.tld/bbpress) drops them into the bbpress install. If this happens, visitors will see the theme from that blog and not blog 1 which is where I'm assuming one would want the footer and header to be coming from.
Come to think about it, you;re still going to have to make the blog_id call even if you place the forums into their own subdomain as it'll have no idea what header or footer to call.
Unless you;re trying to do bbpress for all of your blogs as a subdirectory. Then it's moot as you'll want whatever header and footer is being used for those blogs.
Maybe if some specifics and links were provided as to the setup....