Don't believe there are any crabapples that are poisonous... Not sure how appropriate any particular one is for wine making, some are tart... Some are sweet... Google reveals many crabapple wine recipes, lots of posts here too
Crab apples are fairly easy to come by. They don't taste all that good fresh, but still make a pretty good wine. I've found some trees have better tasting fruit than others, I'd suggest sampling a variety of apples from many trees. Most recipes call for the addition of water, so a strong flavor is usually beneficial.