I am very suspicious of 0% pools. Running a large pool is full time job and computing and data center space isn't cheap. While I suppose there are people that are willing to work 10 hour days for free, and spend thousands per month of their own money and hope that donations cover it, it does seem odd doesn't it? Mother Theresa of Bitcoin?
Add in that pools are now multi-million dollar business's. A pool with say 15% of hashing power has revenue of $219 million per year. (30 blocks a day, 365 days a year, $800/coin)
How many CEO's running a $219 million dollar business would do so purely on donations and cover expenses out his own pocket?
How would it be done? Withholding blocks or withholding shares would be detectable (although you could mask shares by not reporting %'s instead exact numbers). The maifia solved this problem long ago. Skimming. The easiest way to have a dummy "house account". Credit 1 dummy share for every 100 shares would dilute the earnings overall by 1% and deliver $2million a year in earnings.
Creating a dummy share for every 1,000 real shares would pay $219,000 a year in earnings. (plus donations)
A skim of $2million, or $219,000 well within variance and luck and virtually undetectable.