Oops. I should have tried it first.
When I drag the alias into a Notes document, Notes properly shows the attachment type:
However, when I go to open the attachment, I get an error indicating that the file is already open in Mac OS X.
I use this capability all the time with Lotus Notes on Windows. Works great. Next to doclinks, this is a powerful feature for managing information that resides outside of Lotus Notes.
Unfortunately, it doesn't appear that I can do this with Lotus Notes on the Mac.
I told my client I would reach out to the Lotus Notes Community to see what I could learn...
Please post any feedback below. Thanks!