I'm slightly confused.
If you want the OpFor models to show up, you need to unpak them to the game folder, like you did with the HL models, and get a version of the FGD that has the studio tags for model viewing. I'm not sure if there has been an OpFor FGD released with these tags, so you may have to do it yourself. This link:
http://collective.valve-erc.com/index.php?go=hammer_betahas instructions on how to add these studio tags to your FGD and to enable model support on FGDs that do not have the tags included by default.