The rationale for placing ES adapters close to the resource was, I believe, that the network traffic between the adapter and the resource was much greater than between the adapter and the broker. By placing the adapter close (in terms of network hops or network latency) to the resource you improved performance by reducing the requirement for network bandwidth.
Theoretically, you could accomplish the same thing by deploying a light weight IS instance near your resource and then having that IS publish messages to a broker to which your primary IS instance was connected.
I would probably use this approach only if the resource to which my adapter connected required a lot of network bandwidth and if my integration application was experiencing performance problems that had been proven to be directly related to poor network performance and not to other factors such as poor application design.
There are many benefits from having adapters run in the new Adapter Run Time (ART) as part of Integration Servers instances. Better performance from improved connection pooling and connection management is one and improved ease of administration via web-based Administrator pages is another. Of course, being able to write your integration business logic using Developer (with 6.x adapters, anyway) doesn’t hurt either.
Mark
#webMethods#Integration-Server-and-ESB