No, Service Broker uses conversation group locking to ensure that two
threads aren't processing messages n the same dialog simultaneously.
Obviously if two threads were processing the same dialog, message ordering
wouldn't be possible.  In addition, the locks were extended to groups of
conversations to be locked to handle the problems created by related
messages from different sources being processed simultaneously.  This is
different than the locking for dialog ordering.  Bottom line, Service Broker
ensures message ordering within a dialog but it does nothing for the
ordering of messages between dialogs in a conversation group.  In fact,
messages from different dialogs within a conversation group are not
generally delivered in the received order if multiple messages from multiple
dialogs are received.