Ponzi's DO make people money.
Look at the Madoff trustee, he's been working for the last several years clawing back PROFITS from the investors.
So it's very possiboe for someone to buy into the scam today, make money for several months, or even years, and then withdraw all their investments. Plenty of Madoff clients did just that.
Of course, not everyone can get their money back as we all know the basics of the scam. If there's a trick it's to get onboard quickly, make some good cash, then get the hell out of town.
So Flash, it's not surprising your mate is making money, but it will be very surprising (in a similar vein to the sun rising in the West) if he keeps making the money forever
My advice would be to bank the quick cash, withdraw everything and laugh at how he invested in a ponzi and got out with some nice profits.