Simply put, no. Both instances will have their own security domains, user authentication etc and the Qlik Sense hub isn't modifiable to the extent you could integrate it in the manner you are suggesting. Instead what you can do is create a web page that includes your access to both instances and presents all the apps you have access to. How you would set up the security to make this a nice seamless process is a bit beyond my skills though from what I know it should definitely be achievable.
Another potential option, depending on your architectural constraints, would be to automate a process of app export / import and publication for the shared apps between the two sites. This is probably the way I would go.
Cheers,
Rod
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