I think you will need to be fairly explicit about which tests you import. You might fail superclass tests of an overridden function, or simple ctor tests which may have the namespace hard coded, not anticipating this kind of use.
Do you have a mechanism to obtain the superclass's tests? Most module installations don't install their test suite to the system, but only run it from the build directory, blib'ed. If installed from CPAN, the source tarball is around in somebody's .cpan directory, but another user may not be able to see it.