I started nslcd in debug mode: nslcd -d
and saw in the statements that it was looking for objectclass posixAccount. All the entries in my LDAP were of type inetOrgPerson. I had to include the nis.schema in the slapd.conf file, and then add posixAccount as an auxiliary objectclass to each entry. Then, I could finally use getent to see accounts inside LDAP.
Cross posted here: