Seems he's fine with other dogs once he realizes that no one's hurting him, but his overly fearful reaction confirms what I was worried about - being taken away from his litter at only 6 weeks old, he missed out on a critical socialization period with his litter mates. Thankfully, he did very well in daycare, during the hour I popped by to visit on my day off. Instead of screaming his head off this time, he was nervous for about five minutes, growled at the dogs that got right up in his face, but didn't lash out. In no time though, Bella the Beagle took a liking to him, and he was running around and playing like a puppy should. He was even curious enough to check out the much bigger dogs, like Bentley the Great Dane/Greyhound mix, Argos the Rhodesian Ridgeback, and Rogue the Rottweiler.
I'm going to bring him into work with me every day that I can now, as long as he's still small enough to fit in his carrier, to be taken on Skytrain with me.
Here's a video of Jango playing with Drazz. :3