Writing frontend tests with selenium is a lot of additional work to set up client nodes which actually run the tests. With http://casperjs.org/ this is made really easy, as this works headless, so no additional setup is required (which fits to the PHPCI way of testing). They produce a custom output on the command line, but there is a Ticket to support TAP already. It would also be possible to use their xUnit-XML output feature (it's already there) to integrate this as nicely as PHPUnit.
Writing frontend tests with selenium is a lot of additional work to set up client nodes which actually run the tests. With http://casperjs.org/ this is made really easy, as this works headless, so no additional setup is required (which fits to the PHPCI way of testing). They produce a custom output on the command line, but there is a Ticket to support TAP already. It would also be possible to use their xUnit-XML output feature (it's already there) to integrate this as nicely as PHPUnit.