I do develop in scratchbox, and rely mostly on the test suite to check that I didn't break anything.
dpkg-checkbuilddeps: Unmet build dependencies: libqtm-contacts-dev (>= 1.2.1+201) libcubi-0.1-dev (>= 0.1.14) libcubi-0.1-tracker-0.10-ontologies-dev (>= 0.1.3)
Ione possible hack (just thinking out loud, untested) would be to just change the soname so that it gets scanned *before* the normal libqtcontacts-tracker.so (name it libaaaaa.so). The second "tracker" contact manager should then be ignored.
I Future version will have an automerge button that will partially solve that issue, it however stays quite conservative in finding merge candidates. Having a third party merge application would be a good idea too (one that would do interactive merge, vs. unattended for contacts app). You might want to look at the libqtcontacts-extensions-tracker lib then, which has a merge request function ("merge" is not a stock qt-mobility operation).