Can someone travel visit the U.S while waiting for a Green Card application through his sister?

Whether someone can travel to the US as a tourist while waiting for a green card application through a sibling to become current for visa issuance depends upon his or her intention upon entering the country. In your case, the subject already has a 10 year tourist visa. In all likelihood, he would be allowed to continue visiting as long as he did not abuse the visiting privilege and stay here longer then he stays in the home country. We have also seen situations in which US consulates have granted visiting visas to those who have sibling I-130 petitions filed on their behalf if the consular officers are convinced that the applicants are bona fide visitors and not intending immigrants who would abuse the visiting visa.Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.  

Generally not.  Once a green card application has been filed on someone's behalf, they are considered to have immigrant intent.  Someone who intends to immigrant to the US can only enter the US on an immigrant visa (a visitor visa is a non-immigrant visa).