You can create a smart folder that contains them all if you have a mix of imported and referenced ones. Those images and videos get tagged with a tiny icon.

You can manage media in Photos without importing.

Referenced items have a special mark on them that looks like an arrow pointing out of a rectangle (see figure below). To set that option in Photos, go to Preferences > General, and uncheck Copy Items to the Photos Library.

That’s not precisely what Todd wants, but it’s an option some people employ so that Photos only has thumbnails, modified images, and other data inside its library. In the Photos app, by reference: Photos in macOS can work on images without importing them, letting you keep your organization without copying everything. Adobe offers it by subscription in app/cloud storage bundles that start at $10 a month. You can import media directly into it, and it will create folders for you as well. It’s my go-to app after Aperture was killed, and I find it a great editor and a reasonable organizational tool. Adobe Lightroom: Lightroom can reference media files anywhere on any attached drive, so you don’t have to consolidate them.

Combine mac photo libraries