Think of leased HD channels sort of like the leasing of an office building. You might lease to a lawyer, a doctor and an accountant, but not know anything about the law, medicine or bookkeeping. About all you have to do is make sure the tenant is not making illegal use of the space.
A radio licensee is responsible for the content of a leased HD or SCA channel. Usually they put in the agreement something about having the content monitored periodically by a third party for content, with the requirement that it meet all FCC rules and other laws and regulations.
At one time, I worked with a station being leased over several years from the Gene Autrey trust; they even had a person on premises who understood Spanish and listened to samples from the logger of everything we did. It was part of the licensee's responsibility of maintaining positive control over the license.