On the question of whether Paul affirms the propriety of “baptism for the dead” in 1 Cor 15:29, Protestant G.G. Findlay, in the Expositor’s Greek Testament commentary, wrote:
In following up 1Co 15:29 with the words of 1Co 15:30 (τί καὶ ἡμεῖς κινδυνεύομεν;) P[aul] associates himself with the action of “those baptised for the dead,” indicating that they and he are engaged on the same behalf (for καὶ ἡμεῖς associating “we” with persons aforementioned, cf. 2Co 4:13, Gal 2:16; Gal 4:3, Eph 2:3, etc.). (G. G. Findlay, St. Paul’s First Epistle to the Corinthians, in W. Robertson Nicoll, ed. The Expositor’s Greek Testament, Volume II [Grand Rapids, Mich.: Eerdmans, 1970], 930, italics in original)