Pattern is a native AI pattern with bitmaps placed above it. PSD, TIFF, and PDF images are CMYK. PNG and GIF created via Save for Web in Photoshop. TIFF images are layered TIFFs. File created by opening new PS document with transparent background and a simple brush stroke was created, then the file was saved. No special alpha channel consideration was taken into account. This also doesn't take into account the use of clipping paths -- which would further extend the range of transparency in bitmaps, albeit masked transparency rather than alpha transparency. In addition, the 16bit images are flattened to 8bit upon placing into Illustrator, but as you can see, the transparency holds up.
All this is somewhat moot due to the fact that PSD files work flawlessly for 99.9% of files and there's never any reason to use another format anymore, especially if you are working within only the Creative Suite applications. If you are bound to Graphics Converter,some limitations you are seeing may be due to that application, not Illustrator. The only thing I use GC for is multi-page TIFF images (which Photoshop REALLY needs to add support for.)
thanks for this extensive treatment. I did not mention that yes, PSD also worked, but in my example the PSD files were about 6 times the size of a compressed TIFF, or of PNG. Also, I only have PS Elements which does not support CMYK (Elements is ok for what little work I do in PS), though in this example any colour system is ok because it is 100% grayscale work (refurbishing cardboard model sheets of navy ships- the German satiric writer Ringelnatz once said "In the navy, you salute anything that moves and paint gray anything that doesn't.")
So it seems that I have still some options I did not try yet. I'll do the examples you posted and keep exploring