In accord with what Larry said, most Zydeco will be in the pull, or key of F. I would just play an open, or choked F and slide up to the Bb when needed.

Capo the first fret and play in the A position. That's a great sound for a low accordion...

In the "for what it's worth" category...

Last week, I had a party gig. We use different guitar players from gig to gig, and I noticed that the guy we had that night was using a capo on his electric guitar. Since I use an Bb single row, and an F-Bb-Eb triple row, many of the songs end up in the key of F. Not surprisingly, the capo was on the first fret. I did not notice any ill effects from the use of a capo on an electric.

I can't recall any other electric guitar players I have worked with using a capo, but I don't have a problem with it.

Hasn't Keith Richards always used a capo on his guitar? I remember the first time I noticed it, and I think he had it up pretty high on the neck - like on the 7th fret.

-David