No, unfortunately this doesn´t work:
Error: Member::inGroup(): Wrong format for $group parameter
At line 731 in /home/reisueber/domains/reisueber.eu/public_html/projekte/cms-silverstripe/sapphire/security/Member.php
user_error(Member::inGroup(): Wrong format for $group parameter,256) line 731 of Member.php Member->inGroup() line 33 of Workshop.php Workshop->canEdit() line 1240 of TableListField.php TableListField::permissions_for_object(Workshop) line 736 of ModelAdmin.php ModelAdmin_CollectionController->getResultsTable(Array) line 759 of ModelAdmin.php ModelAdmin_CollectionController->ResultsForm(Array) line 652 of ModelAdmin.php ModelAdmin_CollectionController->search(Array,Form,SS_HTTPRequest) line 329 of Form.php Form->httpSubmission(SS_HTTPRequest) line 143 of RequestHandler.php RequestHandler->handleRequest(SS_HTTPRequest) line 161 of RequestHandler.php RequestHandler->handleRequest(SS_HTTPRequest) line 147 of Controller.php Controller->handleRequest(SS_HTTPRequest) line 161 of RequestHandler.php RequestHandler->handleRequest(SS_HTTPRequest) line 147 of Controller.php Controller->handleRequest(SS_HTTPRequest) line 282 of Director.php Director::handleRequest(SS_HTTPRequest,Session) line 125 of Director.php Director::direct(/admin/workshops/Workshop/SearchForm) line 127 of main.php