Purely hypothetical...but it seems to me that if one runs in certain circles, one would know plenty of people willing to pay 90, 80, or even 70 cents on the dollar to clean/hide their money. Maybe I'm missing something, but a steady stream of dirty funds wanting to be cleaned would certainly allow pirate someone to pay his 7%/week by running a BTC laundromat - no ponzi necessary. Further, I think running a laundering scheme via BTC would be pretty durn complex...i.e., it couldn't be unwound quickly/easily/without significant loss if something unexpected occurs.
None of these require borrowing funds at way above fiat market rates over anything but the very shortest time frames. None of these require taking the huge exchange rate risks that Pirate takes by having debt denominated in an unstable currency. None of these work if your cash flow rate is forced by these kinds of exponentially increasing interest payments. Basically, if you can afford to borrow money at 3,000+%, your first priority would be paying down that debt.
The idea that he had some business that was so profitable that paying 3,000% was doable translates into an argument that Pirate had so much money, he could afford to needlessly give it away to people. And the people he picked to be the beneficiaries, for some reason, are people who would invest in something that looks exactly like a Ponzi scheme.
If you put your keys in your desk drawer, there's always a possibility someone moved them. Normally, we ignore this possibility because the odds of it happening are low and the affect it has is small. However, if my life depended on the keys being there, I'd probably check them. For unlikely events, you can assign a rough probability and ignore them unless you have some situation where their affect is dramatic.
If I had to assign a probability to Pirate being something other than a Ponzi scheme, I'd make it less than 1%. Unless I'm dealing with something that has an affect by more than a factor of 100+, I can ignore this possibility. If I was going to make some decision where I'd be killed if Pirate wasn't running a Ponzi scheme, then I'd have to consider the possibility that he's not. I have yet to encounter a situation where I can't ignore that possibility.