I think it is OK in a male-female duet for them to have different intonation. Because they are not trying to sound like one person. Roberta Flack and Peabo Bryson also had different intonation. The ultimate case of very different intonation is Somewhere Out There by Linda Rondstat and Martin Ingram. Totally different intonation. Although in that case, I really think the difference was too much.