An updated ExpressionManager demo now shows that EM can
(1) show/hide all question types
(2) support group.php and survey.php (even including dynamically changing summary reports)
(3) It properly NULLs out single text entry fields, but isn't doing so yet for checkboxes, radio buttons, or array questions.
I have uploaded that demo as version 1.1 to http://www.limesurvey.org/en/additional-downloads/Surveys/ExpressionManager-Demo/ . You'll know you have the new one if the Submitted On date is 30.Jul.2011