The pouch is a rather small reservoir for holding stool, and it can never in any way compensate for a colon. It is your small intestine that assimilates to extracting more water from your stool over the years.
Probiotics help some people while others have strong resentments against them. It may depend on the kind of probiotics you are taking and the condition of your intestines. In the end there is only a small percentage of the bacteria living in the small intestine compared to the colon, and due to a different pH value and other circumstances it will probably be a different milieu.
I take probiotics myself every day, at a normal dosage only recommended for common supplements. If I wouldn't feel it is any good for me I would leave them. Those probiotics, even if it's more than 20 different bacteria stems, could never replace the diversity and function of a large intestine's microbioma. Where there are bacteria with antiinflammatory and pro-mucosal effects, not only a collection of mostly lacto- and bifido-bacilli, aerobic bacteria that are regarded to be useful and harmless.
It is difficult to say what probiotics do for us j-pouchers. Perhaps one effect is to block harmful bacteria's overgrowth at the end of the small intestine and in the pouch, where there is little movement of the stool and good conditions for bacterial reproduction.