Both have pros and cons.
Separate hangfire means that you have to look at 2 dashboard to look at the status of all your jobs. Easier to manage
Another instance of hangfire means that you have to share the interface between the 2 instances since any worker can pick up a job to change it’s status to enqueued. that can become a problem because if you update the interfaces you’ll need to deploy all the hangfire instances.
Personally, I would go with separate hangfire because we’ve started to have problem because we had 6 hangfire instances and everytime we had to change the interfaces, we had to redeploy each of them and sometimes we forgot to deploy one and it would crash the jobs of the other worker since the interface wasn’t compatible with the serialized job.