Hello Imra,
There are some features that SOI has that UIM is not capable to offer, UIM has the concept of CI and the concept of group, but it does not have the concept of business service or the impact service modeling feature, so, you will loose all the functionality related with business services, which is the main SOI focus.
On the other hand, you can create in UIM custom scripts in lua, to enable business like rules on the alarms, for instance, if an application server A is down, and suddenly a second Application server B gets down, create a third critical alarm saying the service is down.