It looks like you got this answered over at the emc forums. http://community.emc.com/message/746653#746653 (reported answer):
"I've just confirmed that DITA 1.2 is now supported with XML Transformation Services 6.7 SP2 P03 (included in the Content Transformation Services Patch 03, 6.7 SP2). This patch is downloadable from the Documentum download center."