Quick update - Jabba is doing really well! He's been out for a few hours each day while I watch. The ducks, goose, and one chicken now seem to have no problem with him, and the one chicken is being mean still. I'll definitely be keeping a very close eye on him for at least another week and not leaving him unsupervised with them. Hopefully the chicken warms up to him. I know that they can do a lot of damage.
I feel like he needs at least one other call... he stands at a distance and just watches the other ducks, then chases them when they walk away. But he never gets close to them. He also tends to just go off by himself. I'm afraid that he won't assimilate into the flock. I feel like, if he had one or two female calls, he would just make his own little separate flock.
He's way too small to get in the pool on his own, so I've left a glass baking dish (about 3 inches deep) filled with water for him to splash in. I imagine that the future ladies would also not be able to get in the pool. Or maybe they'll be like Jabba, and just want to roll around in the mud and avoid the water altogether