This depends if the waiver was approved for his criminal cases or for unlawful presence. In either case, the application might be under background clearance or supervisory review.
If by "El Salvador" you mean US Consulate in San Salvador El Salvador you should consult with an attorney and this discuss the case in a confidential consultation to determine what issues if any may exist. Many times the I-601 even if approved may take awhile to get to the consulate and an attorney's assistance is highly advisable.
No attorney-client relationship is created or implied by this communication. To contact this attorney see his profile; attorney number: 281-733-2875.