There's a few things going on here.
First, Import Agent currently does not have the functionality to generate pages from PDFs. PDFs are not OCR'd in the same way that image files like TIFFs are - instead it's handled more like how electronic files like Word Docs are. If there is a text stream present and you run generate text, the Client will generate a text stream, but not images. If you run generate pages, the Client will generate both the image pages and (if selected) the text itself. We're looking into adding this functionality to Import Agent, but it's not presently there.
When you look at the image in the client, is it showing up in the Image pane, or the Electronic File/PDF pane. You can generally tell by if it has an adobe reader toolbar in the pane. If it's the later, you don't actually have 'image pages' for this document in Laserfiche - instead it is just displaying the original PDF in the Laserfiche Client through an Adobe PDF frame. Without an image page, the Laserfiche Server cannot provide search highlights on the image.
In the Client, are you running Generate Text or Generate Pages? Try running Generate Pages and you should see actual image pages created and then get the search highlights.
As to OCR'ing through DCC, that only OCRs - it doesn't do text extraction. As such, it's not relevant to generating text from PDFs that don't already have affiliated image pages. That said, all Avante and Rio users currently have activation keys for the 9.1 Distributed Computing Component preview release with OCR, but you will need to be using Workflow 9.1 to use it.