I know nothing about Reunion, but this doesn’t sound like a “shortcoming”. Most apps behave that way. If you move a file that DEVONthink indexed, then DEVONthink loses track of the link. I realize that it’s a frequent request to have DEVONthink track indexed files as they move around the file system – but, IMO, expecting an app to keep track of the current location in the file system of every file that app has been made aware of is a rather expansive (maybe also expensive) view of the app’s responsibilities.
I think Jim’s example is the way to go – though because of the Reunion dependency I suggest that the “Images” group in his example (the equivalent of @T_Smith’s Pictures repository) be an indexed group and not stored inside DEVONthink. Except for the images, all the other genealogy files could be imported into DEVONthink and managed there. This case blends well with @Allsop’s recently posted genealogical research use case.
Of course, I’m not the one who’s being advised to revise the data relationships in @T_Smith’s 150 folders and subfolders in order to follow my advice 