This will depend upon the "load balancer" policy that you're using, but if you go with the ones that ship with the esb then it'll try to send to the other instances if the initial send fails.
Apologies but I am still a bit confused. Will it go to the DLQ first or will the other service instances be tried first and then message the moved to the DLQ to await further retries.
It goes to the DLQ after all possible options have been tried. Check out the docs and if you think they are not clear then please raise a JIRA against them.