In the article, it mentioned that Oncor was Energy Future's electricity arm, and that it would "probably be split" from its power-generation business, hence my question. Is Oncor not part of Energy Future Holdings?
To my knowledge Oncor is not part of EFH. Though I could imagine they were left with some kind of stake after the split. More specifically though, Oncor is only the delivery side. Basically meaning, meters and maintenance. Retail providers contact Oncor to have service started. Oncor then send back usage data which the retail side use to bill the customer. If there is a problem, say a line down, Oncor will dispatch the technician.