Well I would hesitate to give a 100% answer without seeing it for myself...So, specifically, a PDQ / Wallstreet / original PowerBook G3 running Mac OS 9 or earlier could still do the job? I just want to be 100% sure
Based on my own memory, and supported by this article: http://chrislawson.net/writing/macdaniel/2k0329.shtml - I believe all Apple-manufactured 1.44MB floppy drives are capable of 800K. I know that Mac OS X has serious limitations with floppies, but Mac OS 9 has full support up to the latest version, I'm 100% sure of that part. I would doubt that any USB floppy drive can handle 800K, and the article reminded me that Imation SuperDisk drives and rebranded LS-120 drives also can't handle 800K.
So my feeling is that if the PowerBook has an Apple-branded native floppy drive, and not some internalized USB connection, I would expect it to handle the variable motor speeds and GCR encoding required for 800K support.