According to this
http://forum.naruto.oasgames.com/en/forum.php?mod=redirect&goto=findpost&ptid=16370&pid=112694&fromuid=27049
Transfer of account is not against the rule, and I assume if perma transfer is ok, temp ones are as well
However, if said friend ALSO have an account on that server, then it might count as violation of multiple account on same server rule, and that is against the rule

So in theory, the "safe" way to do this is find a RL friend to take care of it for you, or if you play on multiple server, have friend from server A to take care of your server B while friend from server B to take care of your server A and so on.