Investing in a ponzi is gambling as you are investing into something in which the outcome/result is unknown.
Putting money into a ponzi isn't an investment, then, is it?
It would only be classed as a legitimate gamble if you were informed prior to 'investing' that it was a ponzi and that there was a risk you would lose your money. Even then it would still need to operate transparently as a ponzi so that all participants were fully aware of the mechanisms of the 'game'.
http://www.investorguide.com/article/12525/what-is-the-difference-between-gambling-and-investing/
Legitimate gamble?
I prefer call these sites "illegal and unregolated" gambling. Legit gambling site are probability fair, so you know exactly the balance between risk and gain. Hyip/ponzis are not probability fair, but this is the part i like most! Balance between risk and gain is influenced by a lot of factors (forums, people thoughts...). What's wrong with ponzi? Ok, it's illegal, So? Try to shut down all ponzis? Some who think to be policemen (with police badge avatar lol;)), try to convince people to never put money in these sites. I'm ok with it, it's a good cause, but not all people are stupid.
I dont care if scrypt.cc has real miners or it's just a ponzi. All altcoins market is a ponzi, and there are thousands ponzi hyip sites. People do what they want with their money.