Different schools of Buddhism use ways of describing things that are completely unacceptable to other schools and some well known masters seem to contradict themselves by using different ways of explaining the same thing to different audiences (Tich Nat Han is a good example). Buddhism has a lot of tolerance for this built in because of the Buddha's attitude toward fixed dogma. The Buddha's own metaphor for this is to describe teachings as rafts - as long a raft gets you across the river it really doesn't matter what sort of raft it was. Metaphors work by mapping the meaning of something onto something else that we are already familiar with. But people have different experiences so while one metaphor works for you it might not work for another person. Therefore, finding the right metaphor is important and it is acceptable in Buddhism for a skilled teacher to choose metaphors to suit his or her audience.
I also think it is useful to contemplate metaphors that do not work for us or that seem to contradict each other. For me, this practice weakens the literal meaning of the metaphors and strengthens the meaning. This is the practice that I use to approach the relationship between Buddhism and Christianity. However, just as it is wrong to force metaphors on others it is also wrong to force practices on others. Practices should suite the current needs of the individual. For some Christians and Buddhists, this practice could be harmful, or at least irritating. This is because it messes with metaphors that are working for them. So if someone feels strongly that these two religions cannot be mixed and that one is better than the other, they probably need that right now, possibly that raft will take them to the other shore, in which case it is OK.