Rather than using some other tool, you could perhaps leverage using TextRecognition or possibly MSAA. It may also be possible to use Object Mapping to map objects to ones that are supported.
There is no current, as far as I am aware, direct integration of TestComplete with Sikuli. Basically you'd be having one tool drive another tool which, while feasible, doesn't make much sense. I think you'd be better of, if you have TestComplete, to use one of the options I've described above. I've actually managed, using TextRecognition, to automate a "green screen" terminal using TestComplete so you should be able to do any Windows based GUI through it. :)
