You can use pwcheck for SASL PLAIN/LOGIN mechanism by
building Cyrus SASL with pwcheck support and then adding:
pwcheck_method: pwcheck
in /usr/lib/sasl/slapd.conf (slapd's SASL configuration
file).
If OpenLDAP is configured with --enable-spasswd, then
one should be able to use "{SASL}user" userPassword
schema to use Cyrus SASL facilities for authenticating
the user.