I don't know if there needs to be a true dependency; e.g. a "DeployersCompletionService" that depends on each deployer ServiceName that gets passed to SomeAppropriateContext, and then deployments depend on that. Problem with that is you remove some minor subsystem that had a deployer, that results in DeployersCompletionService stopping, which stops every deployment. Oops.
A listener mechanism is more flexible, but if you do things concurrently we'd need to be careful about races, i.e. the deployer is started before we listen for it, so we don't get a notification. Not sure it's worth it.
Or were you thinking registerDeployers has to do the actual deployer creation, addition to chains, etc?