I also know of a company who does this. The reason in their case is they act as a network concentrator, bridging hundreds of client IP spaces, so this helps them avoid conflicts with their own space without having to NAT constantly. There is still a lot of NAT for the more common ranges.
The fact that the network concentrator co uses DoD v4 address space to avoid conflicts implies that their clients are bringing v4 addresses, so IPv6 is utterly irrelevant in this situation.
