Originally it was allowed. In fact, I can't seem to find a law that says otherwise. I can find these laws though:
http://boards.nexustk.com/Law/Dalnum04100168.htmlQUOTE
Note: While not condoned, advertisements on any board concerning buying/selling kruna for in-game gold is board abuse.
http://boards.nexustk.com/Law/Dalnum02270154.htmlQUOTE
Sages involving advertisements concerning buying/selling kruna for in game gold is not allowed and can result in loss of sage.
Which means, you can do it, but you can't post about it or sage about it. Using shouts, whispers, group chat, n-mail, clan chat (And its varients), or even NexusForums to buy kruna seems to be allowed. (Post it on the questions/requests board if you're going to start doing it)
Technically, both laws say you can't buy/sell Kruna, which doesn't necessarily prohibit using the boards or sage to buy Kruna
items, gifted to yourself. But that's not a loophole I'd like to test.
Based on all that, I think I'm now in favor of this. Plus, having a legal way to gain nexus gold with RL money might hamper illegal transactions, while helping Kru stay afloat.