To me this sounds as if the schema extension from this cool soultion has been installed at some point and then it has been uninstalled without first checking that the attributes are not used any longer. From previous experience with slapd a suggest that you check slapcat | grep -i sudoHost, i.e. with a case insensitive search, as slapd shows unknown attributes in capital letters.
OTOH, this could also be just a client that specified (sudoHost=foo) in an LDAP query. So let’s go back to the raw data instead of guessing: When you run “gdb /usr/sbin/slapd /core” you should check the output of the following command in gdb:
thread apply all bt
This should output the backtrace of the state of all threads of the process. One of them must show the trace where the abort signal occurrs (probably __GI_raise will show up there). It would be interesting to see the backtrace of that thread, so what function calls happened before that (i.e. in the frames “above” frame #0 of that thread).
Probably you should at least run “univention-install slapd-dbgsym” before, so gdb is able to resolve the symbols in the backtraces.