I just tested Javadoc 1.2, 1.2.2, 1.3 and 1.4 -- all test out
that the -link argument is relative to the destination directory.
(even though the 1.2 documentation is silent.

Note that the first argument to -link and -linkoffline are the same.
It happens that it would be unusual for -linkoffline to have its
first argument be relative (because -link would normally be used
in that case).