Yes. They're two different people. A social worker will evaluate the child and make a recommendation for them. However, an attorney ad litem (guardian ad litem) in this case can also do that. An attorney ad litem argues for a ward's wishes, a guardian ad litem argues for the child's best interest.
Yes. The social study evaluator is appointed by the court to investigate the child's living circumstances and make recommendations as to what conservatorship, possession and access, and support provisions would be in child's best interests. An attorney ad litem is appointed by the court to represent the child's best interests. SOMETIMES, the courts make bad appointments in the sense that they may appoint an attorney ad litem for a baby, which makes little sense (although the family code has provisions for it). In Dallas County, the judges are pretty smart and I've always seen them make good appointments. The social study evaluator's recommendations are not binding on the court, but they are very persuasive.