I'm so touched at all the concern for Rebel. I guess I (understandably) over-reacted, because his bloodwork was fine, and his urine culture came back with an overgrowth of a common fecal bacteria, susceptible to an inexpensive, usually-well-tolerated antibiotic.
Rebel has a genetic kidney defect that results in being very susceptible to bladder infections. This is something we are aware of and treating, and I've had one other dog with this condition and am sadly very familiar with it. It's just a reality we have to deal with.
Anyway, the vet felt there was no reason to worry unless he still has symptoms after a couple of days on the antibiotics, and/or if the vomiting returns. If it doesn't, her assumption would be that it was unrelated.
Sadly, he did throw up his breakfast, and I am back in full blown paranoia. But it was chicken soup, and I think it was too hot, and he ate something else later with no problems, so I'm going to try to stave off said paranoia and relax. (Those of you who know me can all laugh now.)
I'll keep you posted! And again, my thanks!