Also adding to @jefferai's comment, we are working on many "better together" stories that include Vault, Consul, and Nomad. Product's like Boundary have a very large surface area in terms of potential features and road map items. There's a lot of great stuff we're currently working, stay tuned!
While we don't have a docker compose example (yet), I think the diagram in our reference architecture for AWS might be useful in visualizing a HA deployment and how a client connects to targets: https://github.com/hashicorp/boundary-reference-architecture
We plan on integrating with Vault to perform transparent credentials injection in the not so to distant future. This is a 0.1 product after all, and we still have a lot to build!