Yes, as long as the source files are unaltered (including copyright notices therein). Your customer may use GreenSock tools (including bonus plugins/classes you got with your membership) only as a part of your Work Product. However, if your customer wants to use the GreenSock tools outside of your Work Product (or make customizations to your Work Product) to resell to their customers, they would need to get their own "Business Green" Club GreenSock membership to cover their usage. If your Work Product is given away freely and you're not distributing members-only plugins, you're golden...er, green...er, fine.
