Use the rpc.nisd to upload any NIS+ data that does not yet exist in LDAP.
Assuming all NIS+/LDAP data mappings have been established in the default location (/var/nis/NIS+LDAPmapping), use the following command.
# /usr/sbin/rpc.nisd -D \ -x nisplusLDAPinitialUpdateAction=to_ldap \ -x nisplusLDAPinitialUpdateOnly=yes
The above would make the rpc.nisd upload data to LDAP, and then exit. The NIS+ data would be unaffected by this operation.
See the nisplusLDAPinitialUpdateAction attribute on rpc.nisd(4).