I don't think that ScriptAlias is what you want to be using. From the documentation...
The ScriptAlias directive has the same behavior as the Alias directive, except that in addition it marks the target directory as containing CGI scripts that will be processed by mod_cgi's cgi-script handler.
Basically Apache looks for a directory called '/home/tester/MyApp/public/dispatch.fcgi/' and every file in this dir is processed through mod_cgi. In this case it can't be found since it's a regular file.
Have you tried using mod_rewrite? My httpd config for Dancer is pretty much the same as yours except I'm using mod_rewrite
DocumentRoot /home/user/src/MyApp/public
<Directory "/home/user/src/MyApp/public">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
AddHandler fcgid-script .fcgi #using fcgid instead of fastcgi
</Directory>
RewriteEngine On
RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-f
RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /dispatch.fcgi$1 [QSA,L]