Netlimiter is an exploit, not a hack. You can use it for cheating, I won't mention how, but ultimately whether or not it can get you punished is a non-issue for the following reason:
Netlimiter blocks your uploads. When blizzard attempts to investigate your computer for suspicious activity, it queries your computer for a report of currently running programs and processes. If your computer can't send this report, Blizzard can't find out that you're running Netlimiter, much less judge whether or not it's allowed. As a result it's pretty much impossible to get "caught" whether it's against the rules or not.
That being said, Netlimiter is what makes getting this title practical. Not using Netlimiter or a similar program is, quite frankly, fucking psycho because it just takes a ridiculous amount of time to achieve relatively little progress in most zones.
Using Netlimiter, it's much easier but still respectable. Took me 29 days. There's room for creativity/skill, though for the most part it's pressing numlock and alt-tabbing to another window.