Accodring to this Dreamhost Wiki Article regarding Frontpage use on Dreamhost, "You also CANNOT use CGI scripts with Frontpage Extensions!".
PHP, running under suexec on Dreamhost, uses PHP as a cgi to run PHP code; I'm surprised that the WordPress install works at all.
The article also goes on to say that:
In short, it is "Frontpage" alone, or "no Frontpage, and everything else" Dreamhost has to offer.