The rate on U.S. Treasuries is a function, among other things, of inflation, creditworthiness of the U.S. and alternative sovereign debt investment opportunities.
There aren't any statistics that track the practice, but Michael Oates, a CPA with Rothstein Kass in New York who advises alternativeinvestment funds, says many hedge funds are allowing U.S. individual investors to come in through foreign feeder funds or are considering it.