When I introduced my yorkie to my friend's GSD we let them sniff each other and we make sure they were both ok with the other. They were acting super excited so we let them go, and they started running around, and playing. We had to make sure Luchi (GSD) didnt run over or pounce on Roman (yorkie) or get too rough.
They love each other! Luchi and Roman were both about 2-3 years old at the time. Luchi had never been around a dog Roman's size, but it's like he knew he couldnt play super rough. With a puppy it might be different because part of being a puppy is learning how hard you can play with something.
You should make sure that the GSD isnt too rough with the yorkie and make sure the yorkie isnt super scared. If the yorkie were to snap out of fear, that could cause the GSD to snap back and that would not be good. They didnt have much room to run around as we were in a living room, which I feel helped because Luchi couldnt run and chase Roman...i wouldnt want Luchi to think Roman was prey. They were always in site, so we could monitor what they were doing. So my experiences have gone good, but I would never let them be together unattended. It wouldnt take much for a GSD to hurt a yorkie. I hope the meeting goes well!
Here's a few pictures of Roman and Luchi playing |