DEVONthink 2 works well as a store of the nouns (files) associated with the verbs at the heart of OmniFocus projects and actions.

Another post provides Applescripts for the OmniFocus toolbar which support a work style in which any OF folder or project has a parallel folder in DEVONthink.

You may, however, also need more ad hoc links back and forth between OF projects/tasks and a variety of DEVONthink databases, folders and records.

DEVONthink to OmniFocus

Select any folder or record in any DEVONthink database, and use
Edit > Copy Item Link (Cmd Ctl Opt C)
this will put a hyperlink into the clipboard, and you can paste it into the note of any OmniFocus element.

OmniFocus to DEVONthink

Drag a project or task from OF into Devonthink, and you will automatically get an appropriately named record with a hyperlink back to the appropriate part of your OF data.

I find that interlinking data in these programs really works very well.