Yes, it is doable using Tribe API documentation to migrate contents from another platform to your community (what you call as bulk-posting contents) and it can be posted on behalf of the bot accounts randomly. However, it needs a knowledge of coding from your end.
If you have not a sophisticated technical team to help you through this process, you have the option to upgrade to Tribe's premium or enterprise plan, where you can order Tribe to take care of bot creation and the content migration for you.
In case you want to order Tribe team to take care of this custom request for you, please be advised that this types of custom requests are only available for our paid customer, and this is not out of the box. The costs vary based on number of the content and the bot accounts you want us to migrate on your community. If you are interested, please contact our support team.