I'd say that yes, it is bad for them. My aunt just bought a house from some smokers and she pained the ceiling 3 times because the nicotine kept stains kept bleeding through. Eventually she had to buy nicotine resistant paint. That's not really based on anything fishy but it gave me some sort of idea of how much that stuff really soaks into everything around it.
On the other hand, one of my best fishy friends, and a betta breeder, smokes like a chimney, cigarettes and plenty of other things as well. In fact, every time I walk into his house I have to take a minute to get used to the smoke. His bettas, and other fish (probably around 30 adults right now), have all been healthy and long lived, so go figure there.