is there a way to modify the ‘capture Safari webpage’ automator action to use the current page of OmniWeb instead?
If you’re talking about the example workflow, just replace step 1 with the appropriate automator action from Omniweb. If they don’t support Automator yet, then you’d have to replace it with an AppleScript action that would get the URL of the currently open document.
I don’t have Omniweb 5 so I can’t check it for you. But you could see an example of an AppleScript based action in the “Convert URLs to Webarchive” workflow.