I also think that, according to the Unix Filesystem Hierarchy Standard
(see e.g. http://www.pathname.com/fhs/) it's natural place would
be beneath /usr/share/dcmtk since dicom.dic contains read-only
architecture independent data.
Recently, I had a discussion about these issues with Joerg
at comp.protocols.dicom and it seems Offis team is going to
fix this in the next release.
In the meantime, I'd suggest the following patch to fix the
DCM_DICT_DEFAULT_PATH problem. (Don't forget to run config/autoall
afterwards to make the configure script reflect the changes.)