One time I added hydrogen peroxide to urine for ear drops, and the urine got a little bubbly.
While I don't know what effect urine has on the microbiome, it would only make sense it has a positive effect, considering the remedies effectiveness on candida. If it can turn an infection around that is said to be prominently caused by a lack of beneficial bacteria, then it would make sense it contains beneficial bacteria (or possibly creates an environment for them to thrive then the bacteria come in on their own).
After my fast I plan to supplement with a course of (just) lactobacillus (on the stool test it said I had no growth for lactobaccillus, and abundant bifido), and add fermented foods to my meals. Personally, probiotics and fermented foods have done nothing for me, or made me feel slightly worse. I have a hunch, that "beneficial probiotics" actually have the capacity to mutate into bad bacteria in an unhealthy gut environment. There's more about that here.