Ego check please. You don't know more than every vet, you don't know this vet, so lets kick that before it starts. Internet diagnoses are pretty humorous. doctor. LOL
You're sitting here telling people about RI, but then you list cultures done for 2 types of RI. If you knew so much you would have suggested fungal as well. Careful before attacking someone on their lack of RI knowledge.
Mites + cold water will make an R.I. worse, especially if it hasn't cleared up fully, it's very easy to regress. If it's a viral RI you're pretty much stuck and every little thing can bring it back on, if it's a really set in bacterial one- antibiotics are sometimes needed to help finish it off, or else it will stick around.
Next time, move him into a small shoebox style container with paper towel as bedding, heat the whole box up, keep humidity high and treat the mites, but deny him a tub big enough to soak in. He's soaking to get rid of mites, which you can kill easily, if he's soaking after that, his humidity is too low.
Water is naturally cooler than air, and if placed away from the heating element, its easy for it to be too cold.