We used an rdbms for our workflow engine (what you are calling jobs) and it works great. We needed to react to state changes and process workflows within seconds, with dozens of workers executing different jobs in parallel. This is well within the limits of any rdbms.
The workflow system itself took a week or so to build along with a client library and our first actual workflow. Trying to add a messaging system on top for push notification would have been crazy. Polling every second for work in the db works just fine for us. I'm sure we could lower that polling interval arbitrarily lower if we needed (we might never get it as low as RabbitMQ but that is fine).
So if your tps and latency needs fit in an rdbms, I would recommend just operating one system instead of two.
The workflow system itself took a week or so to build along with a client library and our first actual workflow. Trying to add a messaging system on top for push notification would have been crazy. Polling every second for work in the db works just fine for us. I'm sure we could lower that polling interval arbitrarily lower if we needed (we might never get it as low as RabbitMQ but that is fine).
So if your tps and latency needs fit in an rdbms, I would recommend just operating one system instead of two.