This is okay, as you can only have one default domain.
This post shows how to enable Active Directory Authentication within the new vSphere 5.5 Single-Sign-On.
Downloading the Software Before configuring an ESXi 6.0 host to utilize vGPU, the NVIDIA software needs to be retrieved from the NVIDIA site and put in a location where all hosts can access it.
There is also a new identity type (Active Directory (Integrated Windows Authentication)) that works without specifying the AD Controllers directly, like the old vSphere 4.x / 5.0 authentication. The whole process is much easier. Either the vSphere Client, the Web Client, or an SCP program to upload the NVIDIA software to the host. The biggest change is that the RSA database has been removed, which eliminates much of its complexity.
With the recently released VMware vSphere 5.5, the component Single-Sign-On (SSO) has been completely rewritten.