1. There is no problem if you join PSC or vCenter to domain using AD integrated authentication or using LDAP. About VCF 4.x environment using External PSC and later you converge as embedded there is no problem to join vCenter to domain.
2. ESXi you can join to domain without any issue. there will be not impact.
3. PSC and AD integration available in VCF 4.0
3. I would suggest you to use VCF guide as best practice.
NKS
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