Yes, as long as it wasn't smelly/stained/ripped/poor quality. I'm a big sucker for quality, so it would have to be constructed well (no loose threads, ripped seams, scratchy lace, etc.). If it was only used once or twice, I don't see the problem with wanting to save money.
It depends on the culture of the country or people. People of some countries rent wedding dresses instead of buying and owning them.
In America, I presume it's better to get a wedding dress of their own. I guess the best option is to find the cheapest dress available. But again, it depends on the girl and how the family thinks about it. If they are alright about it, why not? :)