They won't allow unbaptized people to use the KH for a wedding. If you are approved to use the KH for your wedding, it's kind of a signal to every JW attending that the couple is In Good Standing™, and both of them are Baptized™ JWs.
The JW Ministers™ who perform marriage ceremonies for JWs are not obliged to officiate for anyone who asks them to do so. They have been known to refuse if instructed to do so by the Body of Elders™. And it can be for reasons of Public Reproof™, Private Reproof™ or just because they have an axe to grind against the bride or groom or either family.