There is an active thread about keeping a sidewall (aka bottle) dynamo running in wet weather. Some people have managed to do it. There might be a mounting point on your bike you haven't thought of, such as your fork. I have been pleased with how well old bottle dynamos work with modern LED lights!

The bottom bracket dynamos are notorious for slipping in the wet, though it may be possible to remedy that.

Since you have a dynamo already, I say try it. I put a Sanyo BB dynamo on one of my wife's bikes. She's only run it once or twice, and so far, so good.

I'm also interested in hearing how the reelights work! No experience with them yet.