Mesh UUID

Is there a standard/spec for the UUID used for provisionee devices?

I don't see anything in the mesh examples that indicates a standard UUID format is used. 

It allows the first half to be user generated, then just pulls the rest from FICR->DEVICEID.

In our BLE system, we used the MAC address to identify devices. 

Can we generate our own UUID format to include the MAC address, company id, device type, etc?