Of late, there has been discussion on the Liblicense-L list about how libraries should go about performing interlibrary loan transactions for articles published in licensed e-journals.
Since, in the U.S., print journals are owned, are subject to the "first sale doctrine," and are covered by long-standing CONTU Guidelines, libraries have not had to generally grapple with complex ILL issues for them; however, e-journals from major publishers are licensed, licenses are publisher-specific, and the terms of the license agreements determine if and how ILL can be performed.
Elsevier has clarified for the list how articles from its e-journals should be handled: the article should be printed, and then "mailed, faxed or scanned into Ariel (or a similar system) as means of delivery to the borrowing library." (Ariel is an ILL system that is widely used by libraries to deliver digital copies of documents.)
To recap the Ariel workflow, the digital article should be printed and then it should be digitized for delivery via Ariel.
See the ScienceDirect Interlibrary Loan Policy for more details.