About using a separate volume pool for each Vault
Jobs within the same vault are queued and then run when resources are available. However, if multiple profiles from different vaults run simultaneously and use the same off-site volume pool for duplication, those jobs could all pick the same target media. This selection would circumvent the queuing mechanism and cause undesirable results. (For example, it can cause a deadlock condition when multiple jobs try to use the same drive at the same time).
Therefore, you should configure Vault so that every vault has its own off-site volume pool.