To see if there are registered sex offenders in the area it looks like you can visit dallaspolice.net (I did a google search). Remember, that only counts for sex offenders that have been caught, tried, and found guilty of the charge. In any neighborhood, anywhere in the nation, there can be sex offenders or drug dealers or criminals of another sort who have not yet been caught. If you are looking to find a "safe" neighborhood I would recommend visting the local law enfrocement websites. Due to fair housing standards Realtors are not allowed to tell a prospective buyer that one neighborhood is safer than another.
Prudential Tropical Realty
The reason for reporting where sex offenders live is so that the persons living next to them may be aware of the dangers to themselves or there children.
If they are living next to you then you weigh whether you want to live near them. If they once lived in a property there is no lasting damage as in a dope house.