Is there a way to point Photos to folder instead of importing them?

1. Yes. But don't. I mean, really, really, don't.
2. Not automatically, but you can do things with folder action scripts and so on.

More detail: what you're talking about here is a Referenced Library. In this scenario Photos doesn't copy the files into it's own library package but just references them in their current location. To achieve this all you need to do is go to Photos -> Preferences and uncheck the box at 'Copy Items to the Photos Library'

So far so good, and as long as nothing ever changes - that is, you never move the files, never rename a folder, never migrate the files to a bigger disk you may have no problems. But Photos really does not have any tools to manage this scenario. And especially when the files are on a different disk then should the path to the files change you can find yourself reattaching all the files to Photos... one by one

Also, importing and deleting become multiple steps. If you decide to delete a photo then you first delete it in the Photos window and then go get it from your folder tree and delete it there - and not the other way round. Similarly, importing means you first place the images where you want them and then import them.

There is zero advantage and multiple disadvantages to running Photos in referenced mode. You can, put your Library on the external, if you're worried about space, or if you really have a jones to use a referenced library I would strongly urge you to use an app that has tools to manage this set up. Photos isn't it.

Photos does not monitor folders but you can attach scripts or automator workflows to folders and you can use there to trigger an import to Photos.

Léonie has written a very good user tip on the issue.

https://discussions.apple.com/docs/DOC-250002591

You wouldn't have to remove the referenced library. The additions would simply be added to it. Move a folder of Photos to your place on the folder tree and then import them. They're an addition.

In general, I don't plan on moving the folder at all, or deleting any of its contents

The word that jumps out at me there is *plan*. If everything goes according to plan you'll have no issues. the grief is when something not in the plan occurs...

Yes and no.

You can import photos to Photos without copying them into the Photos Library. Photos will reference the files in their original location. But you cannot simply point to a folder and all photos in this folder will automatically appear in Photos and dropping additional photos into this folder will not automatically update the photos in Photos.

Change where your files are stored in Photos on Mac - Apple Support

It has been this way since Photos has first been released with MacOS 10.10.3 Yosemite and has not changed since then. There are only additional new bugs, but no improved features with respect to referenced files. I think Apple is testing the referenced libraries so step motherly, because this method of importing is not compatible with iCloud Photos.