Do software publishers need to approve the sale of used software to VENDOSOFT?

No. According to the law (confirmed by the German Federal Supreme Court of Justice), the consent of the respective software publisher for the sale of used software licenses is not required.
The copyright of the software publisher is exhausted upon the initial purchase of the copy of its software in the European Union.
You can find additional legal provisions concerning legally compliant and manufacturer-compliant trade in used software HERE.