As long as they are on separate L2 networks then its a valid config. Melange had the concept of "Public" and "Private" blocks, which wern't like RFC1918 addresses, anything in Public blocks could't have overlaps, but Privates could, i'm not a fan of that though. I think that if you want to create a network that overlaps, as long as its not on the same L2 network is no problem. We should probably check with Brad to see what his opionon is.