I don't think that the Domestic Emoluments Clause's concept of "Emolument" goes so far as to apply to the death of a political opponent. Suppose that I'm a manager at a corporate job and the second-most likely candidate for a promotion. If I order a subordinate to kill the most likely candidate and I get promoted, I don't think that the prosecutor would think to add a "prohibited employment compensation" charge on top of the inevitable "conspiracy" and "first degree murder" charges.
(In a previous version of my comment, I thought that the previous commenter was referring to the Foreign Emoluments Clause and cluelessly asked whether there was a domestic version.)
