Sounds like you are going to need to just create a standalone BO or you could use the already existing Tasks since it also has SLAs. We are using Tasks as a standalone object as well as child of Incident, Request, Problem, etc. for those things our Analysts have to log that doesn't fit into any of the major BOs.
I recently had to create a new BO what was similar to Service Requests, and while I didn't have to mimic SLA's, it did need Tasks, Notes, Attachments, and to properly update My Items. Pretty much what I did was recreate the same relastionships to those BO's that Service Requests had and got it to function the same way. It's worth noting that I did have mimic some of the business rules as well so data would update on tiggers.
Given that your Compliant BO is similar to Inicdent, have you explored leveraging existing Inicdent fields? Maybe adding a "Compliant" Service with some Categories? Or maybe add a Complaint flag/ checkbox to the Inicdent BO?
In our old ITSM product we did something to this where we had two different departments that both wanted to use Inicdents but couldn't see eachother stuff (due to an audit finding). Rather than building a new Incident BO I added a checkbox to the existing Inicdent BO, business rules, and form/ grid logic to prevent the other from seeing the Incidents where the checkbox was checked. It worked out pretty well.