No, never! The online directory is protected technically from being compromised, and is considered confidential and proprietary to MIT. Violations of MIT's rights would be grounds for litigation, if the spammer were discovered.
The paper versions of directories -- faculty and staff, student -- are more difficult to control. While they are under the same controls as listed above, if a copy of a directory were to slip into the wrong hands, it could result in the discovery of many email addresses. Investigating claims of this sort would be extremely hard, time-consuming, and likely fruitless. However, in sufficiently egregious circumstances, the MIT Police would be able to pursue such a case.
See related Spam questions on this wiki by searching for the keywords "spam" or "c-email".