There is no specific integration between the two solutions. VxRail creates & manages a vDS in much the same way ACI can - so typically its one or the other with regards to which solution manages the virtual networking. What most customers running both solutions will do is setup VxRail as usual allowing it to manage the virtual networking, then create a read-only VMM domain on ACI. This would allow the Virtual endpoint and hypervisor information to be visible from APIC. There's not immense value from this, but it does provide some limited additional visibility.
Robert
