Mine has been mounted backwards for 15k miles. The belts aren't oriented any specific way- forward or backward- its just that the tread is designed to handle traction forces differently. If its on the rear, it does mostly accelerating, with very little braking (the front tire does most of the braking). But when mounted in the front, the only forces will be for braking, which will have an opposite pull then when in the rear (acceleration forces), which is why I mounted mine backwards.
Oh, and I've seen plenty of rain, including riding across Maine during a record rainstorm, including passing over semi-flooded roads, and haven't felt any reduction in traction. It clears water just fine. I doubt there would be any problem mounting it either direction. If it would make you feel better, turn it around...my next one will be mounted backwards just like this one. But that probably won't be for another 5-10k miles (man, I love the BT45 on the front!!!)