I recall the forum rules saying that our accounts for ourselves only, and that just as it is forbidden to post on someone else's behalf, it is forbidden to have another account. I recall this ban on DLs is also the reason why the rules state to PM an administrator if one desires a name change.
Logically multiple nations with one account is fine provided every player is able to do so according to a game's rules. Of course, no game has legalised this except for GMs, so it's irrelevant in that case.
I do concur that DLs should be harshly punished. They're against not just the forum rules, but the spirit of fairness. Everyone starts off equally in most IOTs, and you should excel or succeed entirely on your own merits, not an extremely unfair advantage.