Can other instances in my AWS account talk to instances deployed by Boomerang?
By default, this is not allowed. Boomerang creates new security groups each time it creates a new deployment. Only instances sharing the same security group can communicate with each other (on all TCP, UDP and ICMP ports) by default.
The easiest way to allow communication between your instances and the instances created by Boomerang is to place your instance into the VPC created by Boomerang and to assign it with the same Security Group as other instances in the VPC. If an existing instance is not in the VPC created by Boomerang then further configurations will be needed.