I don't have a silver one, but I have a license. You can buy the Dragon. But the Dragon Lair can only be built after capturing all of the opponent's Inferno castles. Before that, it cannot be built.
After capturing all the "demon" castles, the Elven faction gains the ability to build a "Dragon Lair".
Sorry for the off-topic, but I call it a "Dragon Hatchery".