Looks like they've copied some of PHP's tests, yes. But being able to run run-tests.php and being compatible aren't quite the same thing, really. It's how many tests pass that count.
Technical side-note: /Zend there appears to be just the tests for the Zend engine (i.e. from PHP's /Zend/tests), while the containing directory contains test folders copied from other parts of PHP (like the standard library)
Not sure how many of those they are actually passing though. https://github.com/hippyvm/hippyvm/tree/master/test_phpt/Zen...