At a customer I am working on the design of vRealize Log Insight. With the authentication objective we can choose from the sources local, Active Directory or VMware Identity Manager. In the latest release (4.5) it is clearly stated that authentication configuration of Active Directory directly from Log Insight is depreciated.
Edit: Unlike some previous information going around, Active Directory from Log Insight directly is still supported. Quote from updated VMware Knowledge base article: Although direct connectivity from VMware vRealize Log Insight to Active Directory is still supported in Log Insight 4.5, it may be removed in a future version.
But I think it will still be very beneficial to move to vIDM sooner then later.