Thank you for your post.
Yes, it is possible to incorporate Saved Finds into a Custom Menu set. As a test, I searched on a Name field for TSGal and saved the find naming it "TSGal". I then created a Custom Menu with the Records menu, File menu and Edit menu (in that order). I made the Custom Menu active, pulled down the Records menu, selected Saved Finds and "TSGal" was active.
If I go into Preview Mode, then "TSGal" is grayed out. Naturally, this menu isn't active under Find Mode or Layout Mode.
I know this doesn't help you, so this could be caused by a combination of menu items included/not included that is triggering this. I would like to see a clone of your file so I can determine the possible cause. I have sent you a private message (top of this page - right side - X Messages) with instructions where to send this file.