Webdav in pavhe does not support to run under different users which is required for secures websites, so it is not possible to access the site files with webdav. For that reason, webdav is only implemented as file storage option and not to access websites.
Which problems do you had with wordpress. My guess is that you just used wrong site options as wordpress works out of the box on ubuntu systems that i installed for several clients. All php based cms system require the php mode php- fcgi and suexec has to be enabled, thats described in detail in the manual. With other php modes, you dont get write access to the site directory which is required by wordpress.