Dunno. What I can tell you is that since Cs3, Photoshop has provided "smart objects" which are essentially embedded Photoshop or Illustrator filesto which filters can be applied in a non destructive fashion. So Photoshop file A can have an embedded Photoshop File B embedded inside. If I double click on the embeddedobect, that item ones up as a separate Photoshop (or Ilkustrator) file to which edits can be made. Re-saving it re-embeds it in the parent Photoshop file. You can apply filters to these smart objects without affecting the original data.
If you think of it being like a series of nested Russian dolls, you'll get the idea. I am certainly certain that GIMP won't support this. The .psd format was originally open and well documented, but it seems that Adobe are being more and more guarded about it, and it seems that it's becoming a closed simply by future f the documentation of it being less and less helpful. I am reading articles that suggest using the TIFF format in preference to PSD simply because it's easier to read and write Note that Adobe support Smart Objects in TIFF files, but, again, whether other apps support these is up to the developers of those apps. I would assume that they are not until proven otherwise.
As far a the OP is concerned, it sounds like they have standardised on Photoshop - supplying another app will require training, file conversion, standardisation etc. etc.. I would think that keeping with Photoshop in some fashion would be more sensible unless the long term plan is to drop Photoshop completely and standardise on another product.
