
Gsds are the same as any other breed in this respect - the sooner you let them off the lead the sooner they will learn a reliable recall. They need to be trained in all situations, and that incloudes loose with distractions. Just ensure that a scuccessful recall doesn't always mean the end of fun - ie, don't call him back to put him on the lead every time. And avoid calling him back if it's clear he's having so much fun with his own kind that he won't obey. The ideal to aim for is that playing with other dogs happens every day so that it becomes 'ordinary' - almost boring! Nothing to get excited about.
:)