Of course the Church hasn’t ruled, but if the Church were to rule when the situation arises, I would say yes: they are capable of forming a natural marriage bond between rational creatures, and sexual relations between such couples (taking Star Trek and Superman at face value) would not be considered an abomination because of the fact that two rational creatures are involved. If I were Pope (and you lot thank the heavens I am not!), that’s exactly how I would say it.
They would be incapable of contracting a sacramental marriage, and if Amanda or Lois were Catholic, would require dispensation.
Further, I as Pope (and you lot, again, thank the high heavens that I am not!) would rule that Spock would also be eligible for baptism, as he would be a descendant of Adam, pointed ears notwithstanding. However, Sarek, being fully non-human, would be ineligible.