The extension will work with modules as long as the module displays the tag text in the page HTML. Once the page has been built and is ready to be pushed to the browser for viewing, the Nice Watermark scans the page looking for any Nice Watermark tags. If it finds any, it replaced the tag with the correct HTML to display the image. So, it sounds like the Zoom module does not display the NWM tag in the HTML.
One work around would be to put the NWM tags on a separate page, like in an article. Then visit that page from the front end. After which, the NWM images will have been created. You can then look for them in the images/nicewatermarks cache folder. Use the image URL to these watermarked images with Zoom. If you are fairly certain that the images will not need to be regenerated anytime soon, you can set the NWM plugin cache time parameter to something really far out like 10 years. This will preserve the cached images. Or, you can move them from the cache folder to a permanent location.
Let me know if you need anymore assistance.
~ Best regards