Did you check out the for-each activity example in the developer's guide section 2.3? It seems to be working fine and is recognizing the for each tag and other related attributes.
Yes this functionality is not in the design window of the Eclipse gpd. This is something like the group activity which you need to embed using souce window. But the tag is very much recognizable otherwise it would have been listed in the problems view. You can try using web based Signavio editor to design your workflows which is a little more user friendly and provides the XOR gateways.