DNS update workflow in SDDC manager does not update the DNS of vROPS.
It will only update the DNS records in resolv.conf. However, the vAPP properties will be left untouched causing the update to be non-persistent.
VCF
This is an expected behavior by design.
Manually update the DNS records of vROPS using the below KB.
https://knowledge.broadcom.com/external/article/322114/modifying-the-dns-settings-of-a-vmware-a.html