If the speaker is amplified and the sound card has center output, it would work. However keep in mind that I can't think of a single game/video player that lets you run in 3 speaker mode. You can run 5 speaker mode and the center would work, but if you're missing the rear channels that's going to cause you more problems than it's worth.
And for other reasons, having a center channel that doesn't match or at least closely resemble the other two in acoustic signature is a bad idea. So the point is it's really a bad idea, don't do it 🙂