Normally when the right to income is contingent upon the happenning of a future event, it is not considered taxable even for a taxpayer on accrual accounting. See Guarantee Title & Trust Co. v. Commissioner, 313 F.2d 225, 227.
The US Supreme Court has also said that money is not taxable as income, even to an accrual taxpayer, until the right to it has become fixed. Schlude v. Commissioner 372 U.S. 128, 137.
A regulation cannot change the law, it can only clarify the law. If the right to receive or keep money is too contingent, it isn't taxable until the right to receive or keep it is fairly certain.
In this case, based on additional information given by OP, it appears that his right to keep money he was paid is subject to a slight risk of having to give it back, but not so contingent that he has not actually earned it yet. So it seems to me that, under the circumstances in his case, he is required to recognize the income in the year received.