The hot path is the time between receiving market data from the network, and reacting to it by potentially sending an order. It's typically a thread constantly polling events from the network card.
In that path the rest of the world does not exist: you are interacting with an exchange, possibly multiple exchanges, and that's it. The rest of the world doesn't exist. No ZeroMQ or Kafka or whatever.
After you send an event, you can set a flag or copy some data structures for another thread of lower priority to do some house keeping. This might include sending an update on some messaging system, yes. This can be something like TIBCO RV, or a proprietary equivalent, or perhaps the ones you mentioned.
But the bottom line is: when doing low-latency, high-frequency trading you don't want to do anything that is not strictly required in the hot path. You must read the message coming from the market, very quickly decide how you want to react (i.e. send a new order or update an order, at which price point, etc.) and that's it. You will in fact even avoid computing too much stuff here; you would have pre-computed as much stuff as possible to be ready to very quickly do a lookup and maybe some trivial computation before making your decision.