There are two issues at hand regarding skydive pilot operations:
1. Legal - just because you don't get monetary compensation does not necessarily mean that you can do it on a PPL. Be very careful.
From skydive magazine
Flying jumpers without a commercial certificate
Q. I think the answer to the question printed in Skydiving #219 about the pilot training required for jump operations was incomplete.
It is true that a commercial pilot certificate is required if the pilot is to be compensated for the flight.
But it's also true that a commercial rating is required if the passengers pay for the flight or if the flight took place for commercial purposes. One litmus test that the FAA uses is, "Would this flight have occurred if the passengers did not pay for the ride?" Rarely would a jump operation pass this test and be permitted to use a private pilot to fly a load.
Passengers are allowed to "share" in the cost of the flight but the question remains. And since the FAA is the prosecutor, the judge, and the jury, in their own court system, they rarely lose. The moral of the story is that even in a club environment, the pilot should hold a commercial certificate and of course the appropriate rating(s). -- Mark R. Williams, New Brunswick, N.J.
A. Just paying for a flight doesn't automatically make it commercial in the FAA's definition of the word. A passenger may pay something towards the direct costs of the flight; he may share certain costs with the pilot. The pilot of a Cessna 182 could, for instance, let people jump from it providing he or she wasn't compensated (paid beyond a portion of the direct costs) for the flight, even if the pilot held only a private certificate.
The pilot and jumpers could split the cost of the fuel, however, and other direct operating costs.
As Williams notes, our sport in the U.S. is almost exclusively pursued at commercial centers, so rarely would a pilot not need a commercial certificate to carry skydivers. At a for-profit DZ, even if the pilot isn't paid, the aircraft owner or operator is. The FARs require a commercial certificate in those situations.
But private pilots may, in some situations, legally haul skydivers.
Skydiving Magazine Queries from December 1999
2. Moral - like I said, most sky diving ops are paying jobs, and you should be getting paid, not doing it for free. Even if you meet the requirement of a CPL. I know how I would feel if a Pilot came willing to work for free and I lost my job as a result.