Do I need to add /opt/trinity/lib/trinity too or are
subdirectories of /opt/trinity/lib automatically found by ldconfig?
No, you need to add any directory outside the 'standard system set' (normally /usr/local/lib, /usr/lib, /lib, and any /lib32 / /lib64 variants your distro may use). Subdirectories are not autoamtically searched to satisfy DT_NEEDED entries. However, the lib/trinity/ subdirectory is not loaded via DT_NEEDED entries but via explicit dlopen(), which does no path searching at all because the path needed is explicitly specified in the dlopen() call.
(And you need to run /sbin/ldconfig.)
I don't understand the full technical aspects of what you wrote, :-) but what you wrote matches the particular error messages I'm seeing.
Although I asked the question, I was leaning toward /opt/trinity/lib/trinity not being necessary in /etc/ld.so.conf because the equivalent /usr/lib/kde[3] never was needed with KDE3 and everything works as expected.
The peculiar thing about this problem is only kword and kpresenter are affected. Possibly there are other "undefined symbol" problems in my builds that I have not yet noticed, but I'm guessing kword and kpresenter are not linking correctly during my builds. I don't know how to debug further or what to look for.
Darrell