If they were in your hand, you would be restricted from playing them. Therefore, allowing them to be played from your discard would NOT be playing them "as if they were in your hand." It would be using a standard Marshalling action to play a card from your discard pile, which Melisandre's Schemes does not allow you to do. If it did (as a replacement effect), you would be restricted to only playing characters from your discard as it would've replaced the standard Marshalling action with this new "from discard" marshalling action. If it did (as adding a new type of action) the "as if it were in your hand" wording would be unnecessary (see my last paragraph).
The game does not allow you to play cards from the discard pile as a Marshalling action. Melisandre's Schemes tricks the game into thinking the card is in your hand. If the game thinks it's in your hand, Fear of Winter applies. Whether or not it would be legal to play out of the discard pile (it would because it's not actually coming out of your hand), the game will never allow you to initiate the action as it thinks the card is originating from your hand.
Now if you're going with the designer's being lazy and not putting, "you may play characters from your discard pile by paying their gold cost", and whatever additional necessary text to actually allow the bypass of Fear of Winter I would agree.