Thinking about it, can it really work the way on Linux you claim it does ? The DHCP server only has the MAC address to identify the interface by, so surely adding DHCP'd alias is just going to get you the same IP address that has already been allocated to the interface by the server ?
In
theory the DHCP server is meant to identify clients by the "client identifier" field, not by MAC address. But now you mention it, I've never tried DHCPing off aliased interfaces, so I don't actually know whether it works in practice with any particular server. (Although the recently-discovered
bug in Receiver Edition, where using the same xid and ciaddr from
different MAC addresses makes the server think it's just one client, suggests that it sort-of might.)
Peter