I think dummies are okay in moderation - if the baby is really upset for example, a dummy might be good to calm him/her down. Or to get them settled just before they go to sleep.
I really don't like it when parents shove dummies in their kids' mouths just for the sake of it - when the kid is quite happy without one! Seems pointless.
Anyway that's kind of going off the subject.
In terms of teeth, honestly I dunno. I had a dummy as a kid just before I went to sleep, but that's it, so not much at all. I never sucked my thumb either. So yes my teeth are straight, but that doesn't help much with your question.
As for Lydia, she never took to a dummy at all. We tried her with one for maybe 3 days and she just never liked it, so we never bothered after that. She doesn't suck her thumb either.
IMO a dummy might be better than a thumb, because you can wean a child off a dummy. You can take it away, hide it, give it to 'Santa', whatever. But no matter how hard you try, you can't get rid of a child's thumb. Much harder to stop a child sucking something that is permanently attached to him/her if you see what I mean.