Monetizing points/miles is fine if you reported the points/miles as income when received, e.g., what Citi does. But, if you didn't, your tax basis in the points/miles is $0 and the reimbursement, when received, becomes income.

First, as an employee, you have a duty to report the reimbursement as income (and pay taxes on it).

Second, as an employer, you have a duty to include (in the case of a US tax payer) the reimbursement as income on a W-2 or 1099 as the case may be.

I find it hard to believe that the paperwork associated with documenting and tracking this stuff is worth any savings which might occur.