It could if an install got corrupted. It's unlikely though. The reason? I have no idea but it is possible.
But since you have an external hard drive I'm assuming for your Wii U games you can just inject the Wii games on the same hard drive as the Wii U without switching any devices that's what we were telling you when we're referring to injecting Wii games. It wouldn't be a dedicated device it would be the same device that has your Wii U games. But if you wanna just install to nand go for it more than likely you'll be fine. Regardless if you install to nand or hard drive you have to use the same program linked several posts up convert the Wii games to WUP installable and use WUP Installer. There you can choose nand or hard drive.