I have that already. my AD is connected to 3 brokers.
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CloudMqtt with encryption
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Local Broker with just username and password
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Remote broker on the same network, without username and password
Theoretically, you can connect to as many brokers as you like. I use OwnTracks, which sends my data to CloudMqtt, and with an AD app, feeds it into a device_tracker component in HA; which is connected to a different Local broker. I then mix it with Andrew’s Home Monitor for home detection, which is also connected to my local broker.
So OwnTracks is used when not home, the other used when home for extra reliability.
Regards