If you're referring to the Mangiamele letter, yes, they can. The pilot on such a flight incidental to employment can accept pro rata shares from each passenger. What those passengers do after that isn't the FAA's concern, so those passengers can claim reimbursement from their employer without the FAA's knowledge or consent. The only thing the pilot cannot do in that case is collect reimbursement from his/her employer for his/her own share of the direct cost of the flight. So, under Mangiamele, the more passengers the pilot has, the less the pilot is out of pocket for his/her share of the flight, which seems to me to encourage carrying as many passengers as possible on such flights -- which I don't think was the FAA's intent in this matter. Chalk it up to the unintended consequences of some FAA attorney twisting the wording of 61.113 all out of shape.
I bit confused here, and at the risk of finding out I'm doing something illegal I'll ask anyway. I take my Mooney on business trips occasionally. The US Government's own Joint Travel Regulations state that I can use my own private aircraft for government business related travel and they will reimburse my expenses at $1 per mile up to the cost of commercial carrier. In my Mooney, that is typically sufficient to cover all of my expenses. Are the US Governments own travel regulations in conflict with FAA regulations?
No, they are not. The JTR's on this only establish the maximum rate at which the government or government contractors can reimburse government employees and contractors for air travel in privately owned aircraft without further justification. However, that does not provide permission for individual pilots who happen to be government employees or contractors to accept that reimbursement -- only the FAA has the authority to approve that.
Further, it doesn't establish that rate as an approved rate for income tax purposes -- that's an IRS function, and the IRS is on record saying you still must justify the actual expense of the flight with IRS-quality records with no "standard" mileage rate authorized as their is for privately owned automobiles. If you collect $200 from DoD for flying your privately-owned 172 on government business on a trip of 100 miles each way on a $1/mile basis per the JTR's (or whatever it is currently), you still have to be able to show the IRS you actually paid at least $200 in expenses for that flight even if you don't have to show your employing/contracting Federal agency. If it didn't actually cost that much, anything over the actual, documentable cost is taxable income. OTOH, if it cost you more than $200, you can deduct that excess expense as an unreimbursed business expense on your personal income taxes. And yes, I've been over this with the IRS and two tax professionals, but feel free to get your own review from your own tax professionals.
However, none of that authorizes you to accept reimbursement
from your employer for carrying passengers when that is prohibited by the FAA even if you can legally accept
pro rata shares directly from your passengers under 61.113(c). So, as I said, on a business flight with three passengers, you can collect 3/4 of the cost directly from the passengers, but you cannot collect the other 1/4 from your employer or collect their shares directly from your employer
even if your employer is the Federal government. I realize that appears a bit of a paperwork dodge, but that's how
Mangiamele reads.
IOW, just because some department of the government is authorized to pay you something doesn't necessarily mean you are authorized to receive it and/or not pay taxes on it. That may sound like a Catch-22, but it is the law.