I seriously doubt there's a specific provision for this. More likely, it's simply the case that erectile dysfunction is considered a covered condition, Viagra is the prescribed medication, and so anyone prescribed it is covered. Probably simply a case of there being no wording to specifically exclude sex offenders from this coverage that everyone would get, rather than wording specifically granting it to them.
It'd be much the same if the government announced a tax break on firearms to the whole country and CNN posted:
"Congress approves tax break to put guns into the hands of gang members and sexual offenders!"
Well yeah, they COULD take advantage of the tax break, along with everyone else, but that doesn't mean it's the intent of the legislation. That doesn't bother a news outlet though. They'll put their spin on it, because their job isn't to report the news - it's to draw in viewers. CNN, MSNBC, and yes, even Fox, all do it. Remember - you the viewer are not the customer. You are the product, and their advertisers are the true customer.