Is Drupal forum module suitable for a massive forum
It depends on how 'massive' is your forum, what level of control you expect to have on the forum and how powerful and well configured is your server. There are Drupal forums with couple of hundred thousand users that work kind of fine, but if your main goal is to have a large and capable forum, you get much better performance and features out of specialized forum software like VB.  

While Drupal forum provides rudimentary functionality, you will have hard times attaining many common specialized forum features like assigning different moderators to each forum, post thanks (which exists in D6 but not in D7), merging threads, banning users for certain amount of time, limiting posts/threads per day, and the list goes on and on. 

The only pros that I can think of is integration to Drupal core, which makes sense only if you already have a Drupal site.