I have recently come across an issue in our new VCF 3.10.x build that when we try to deploy the VRA using SDDC Manager, we get an error that the AD Account we have provided can’t validate with the Domain.
The warning is as shown in the picture below:

Note That I had to change a few details and also blur some details from my environment due to privacy reasons.
The Error basically states that VRA is not able to communicate to my domain lab.com with the service account lab\svc_vra_adm because it is trying to contact test.lab.com instead of lab.com Domain
test.lab.com is a DNS Zone in our actual root Domain lab.com and all our VRA Appliances have the host records added to test.lab.com instead of the root domain.
After multiple tries and VMware support, we got to know that VRA (7.x and 8.x) doesn’t support explicit identification of the Active Directory domain name. The kb article which mentions this issue is
https://kb.vmware.com/s/article/59128
The Solution is to make sure that the host records of your VRA is the same as your ‘Actual‘ Domain, in this case lab.com and then retry the validation using the SDDC Manager with the same service account lab\svc_vra_adm
This time, the validation should pass.