I just submitted a support ticket precisely for this reason: documents (PDF) I scan with Scanabble should be indexed and OCRd within Evernote after it has been imported (for premium accounts, like mine) but this is not occurring.
Searching for content in any of these documents that come from Scannable in Evernote returns zero results, even after allowing Evernote 2 whole days to perform its background indexing processes.
Checkout an example note I uploaded.