IBS is an interesting disease. It is in fact not attributable to a specific cause, and in many instances in psychogenic. It is certainly real, but it not very well understood. In fact, we were always told that is was a diagnosis of exclusion, meaning once everything else it ruled out, you have a dx of IBS.
UC is a serious disease, and a inflammatory disease such as UC could certainly cause hair loss. It would make sense that with this major inflammatory response and cell turnover in your body going on, many of the chemical mediators/hormones would be thrown off, and could easily mess up your hair cycle and follicle growth. Plus, there is the possibility of vitamin/mineral deficiency caused by these disease, which can lead to hair loss and other problems.