Thanks for all the replies! Rhys is most DA on his own turf; we walk through neighborhoods that have dogs running fences, or people walking very reactive and badly behaved dogs WAY too close to us. Off leash dogs are also a huge problem. He actively wants to fight another dog in those situations; there is no back up in him. We have a neighbor with dog that was supposed to be 'friendly' who rolled Rhys when he was about 3 months old. He has hated that dog since then. We have worked on his threshold but he is very difficult to control without a prong collar.
At conformation shows, most of the dogs are under strict control and have no interest in each other-he does just fine in those environments. He can stand close to other dogs, be shown next to them, etc, with little to no problems. He's only had one incident at show; someone walked their APBT by his crate and that particular dog decided he didn't like Rhys, who was resting quietly in his crate. B went after Rhys through the crate, luckily I was close by. Rhys didn't hesitate a second; he made a strong bite and I had to break him off. Luckily he wasn't hurt and I'm good friends with B's owner, he was very apologetic.
He has done lure coursing and weight pull with no issues. Lure coursing, especially, he has been in a very, very high state of arousal and totally ignored other dogs in his desire to get the lure.
I think if I could keep him interested in me and make agility really fun for him, other dogs wouldn't matter. Especially if the other dogs gave him space and weren't interested in him. He's pretty predictable but he has the potential to do some damage so I'm trying to be realistic with what he could do. If the ring is secure, I wouldn't worry as much; he used to barriers and respects them.