Ya, I think it depends on their structure. Many are based offshore (Cayman Islands), however if the manager of the fund is based in the U.S. then he pays U.S. tax rates.
I think the loophole is regarding the carried interest portion of the fund. The manager gets the 2% of AUM (which is taxed at ordinary income), yet the performance fees are considered "carried interest" and therefore taxed at the more favorable capital gains rate.
I'm sure the guys who set up these funds are well versed in the structure and how it works most favorably to the fund and its managers/owners.