Publishing search to a consuming farm - configuring security access to the items being searched in the Publishing Farm

Hi

We are planning to publish our sp2013 Search service app to a SP2010 consuming farm. The question is do we have to add users from the consuming farm to the publishing farm for them to see any search results? Once the Search SA is published is it possible to add users from the consuming farm to sites? If not how will they see any results? Surely security trimming will mean they will see nothing?

Can we add all the users who need to see search results as a group to a Web app policy on the publishing farm? If so then will these users from the consuming farm be able to logon to SP sites in the publishing farm? The aim is for them to consume search only. Will they show up in people picker once the farms trust each other? The farms are in different domains

Thanks

J