A bit late in the game, let me link to this story about Southern Baptist macher Albert Mohler saying that yoga is anti-Christian. He had read the new, very important history of yoga in America. The Subtle Body, by Stefanie Syman, and was moved to point out that yoga is a spiritual practice that may be incompatible with proper worship of Jesus.
My simple answer is: it depends what yoga. Full disclosure: I started doing some yoga classes last month. So far, what I know is next to nothing. But I do know a lot of people who practice yoga, and for some it is clearly a full-blown spiritual practice, while for others it is basically a stretching regimen. Those who read my first book know that I am of the belief that serious religiosity tends to be exclusive: that is, you pretty much know you are a serious Methodist if you are so Methodist that you cannot also be into Buddhism, or perhaps hard-core yoga. Real religion tends to resist syncretism, at least at the individual level (certainly not over time, or at the culture-wide level). And I do know that yoga teachers, at the very least, are very insistent that they have a full mind/body system
So Mohler may not be so far off, if he is talking about the most committed practitioners. But as a blanket statement, that (downward-facing) dog will not hunt.
But seriously, read Syman’s book.