Yes, that is best practice. However, I usually deploy vcenter for my testing and almost 99% of times, I did not add vCenter VM to domain and it worked just fine for me in test environment. Later I use to add domains as identity source in order to give permissions to domain users.
If it is production environment, it is always better to add it to domain.
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Thanks & Regards
Vikas, VCP70, MCTS on AD, SCJP6.0, VCF, vSphere with Tanzu specialist.
https://vThinkBeyondVM.com/about
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