Is it possible to use a page in a Visio doc as a layer in another page in the same doc?
Currently, I'm copying and pasting when I make changes to page 1 into a layer on page 2, but would like it if the layer simply updated.
Yes. Background pages can be used in this manner.
Create a page ("Page 2") and in the Page Setup dialog in the Page Properties tab set the Type to Background
Then in "Page 1" in the Page Setup dialog in the Page Properties tab set the Background to Page 2
Now everything you draw on page 2 will automatically show up on page 1 - underneath any shapes in page 1.