BitComet and Auzureus support own DHT Networks. BitComet should have also to the Azureus DHT network contact.
BitComet supports the DHT standard made by Bram Cohen the developer of BitTorrent. BitComet was the first to implement this standard after it was released in the official mainline client. µTorrent also supports mainline DHT.
Azureus DHT support has been requested before. But its low on the list.