Why does pt-table-checksum gives exit status 0 if slave is unreachable?
pt-table-checksum runs on the master primarily, but as binary logging on MySQL is statement based, the actual calculation statements are being executed on the slave as well. One should then run pt-table-checksum on the slave to check and compare the checksums it can't access the slave from the master. Add the --replicate-check-only option to have it only check for differences based on the checksums already present in the checksums table.