I introduced him to Holly, my senior sheltie mix, and they are doing fine together. No problems. Snyder was nervous meeting her, or at least I think he was. He makes a funny snort sound sometimes and he did that along with some whines. His body posture was also anxious (prancing and trying to stand tall) but they exchanged sniffs and after 30 minutes or so of Snyder continuing to be a little anxious they were sharing the couch together (yes, I do let my dogs on the sofa). I took some video of them taking treats together and have added it below.
I've said it before but Snyder loves everyone human. He loves to cuddle with everyone in our family and he just generally likes to be where they people are. He will use his nose to flip your hand onto himself if he thinks he's not getting enough petting.
Thanks for reading and thanks for thinking rescue. Please keep reading prior posts for more info on Synder.