Hmm that is a tough one... changing files as a condition to a rule.
From a CPU resources perspective...if Hazel is going to do the processing anyway, it might as well offer the option to save it to the file.
Otherwise, depending on one's workflow, the same document could be OCR'd up to 3 times: once on-the-fly by ScanSnap Home for file naming purposes (can be turned off), once by one's preferred OCR app, and once on-the-fly by Hazel.
It could be more efficient if Hazel added the option to save the text to file.
With that said, I did email the ScanSnap Home folks and asked them to consider changing their OCR software to Apple's native (more accurate and faster). They passed the request on to the developers. Might be good for any other ScanSnap Home users to do the same!
Finally, I hadn't notice Preview's ability to export with "Embed Text"...nice find. I'll also start digging around to see if there is a way to automate that export option.