WodPress code doesn't take kindly to PHP input - although there are some plugins that can enable php compatibility (in certain areas). But the nature of Universal Email php code and directory structure would make it difficult and frustrating to try to implement successfully across the entire UE file stucture.
I'm not sure why you wouldn't want to build your custom form with a native WodPress plugin - Search (from the plugins page) for 'Fast Secure Contact Form' - you can configure multiple unique forms that include the standard contact fields, plus up to eight other custom fields - all options are highly configurable, and guaranteed to work with WordPress3.1.1
