The rulings on gatherer specify that a card with no mana cost has a CMC of 0 and you can cast them.
http://gatherer.wizards.com/Pages/Card/ ... eid=426744You can also check around and there are many decks from reputable sources that make use of such combos. Not having a mana cost means that it can't be played normally, but
As Foretold isn't playing it normally, it's an alternative cost just like the Suspend ability itself is an alternative cost ability.
As Foretold should (but currently does not) let you cast those cards with its own alternative cost.