There doesn't appear to be any checks if files are included as:

include '/path/to/file.php';

or

include ( '/path/to/file.php' );

(Repeat for include_once, require, require_once.)

WordPress Core apparently does a mixture of both.

Generally, there is no different between them, except when a comparison is done against it - see Example 4 on http://us1.php.net/manual/en/function.include.php. Otherwise, the ( ) are redundant and can be safely removed.

There is a PEAR sniff that could be used / adapted from.

This was mentioned in the #core-coding-standards channel, so while any addition would go into WordPress-Extras right now, it may be that the Handbook has been updated, so this could go into WordPress-Core standard instead.