In UK and Ire the instruction on the Imodium is to not use for severe UC. From which I deduce that it is appropriate to use it for maybe a mild active flare.
Imodium works very well for my IBS. Slows things down and eliminates gas. I've logged out to a similar website based solely for people with IBS. Their recommedation is that Imodium is okay for maintenance use for mild IBS. "Once a day" use is reported as fine by them. They have pointed me towards surveys showing tht the body in general does not become "addicted" to the drug and neither is there in general withdrawl symptoms. However the body can build a resistance to Imodium as it in a sense performs a function that the body should itself be able to form.
Once a day Imodium seems to be fine for IBS maintenance therapy. Imodium as a short-term reliever of mild IBD symptoms seems okay. If the flare is severe I think it will limit the effectiveness of the drug.