Since firmware 10.x, Axis devices supports MQTT. This is simplifies integration to various systems. However, there are some challenges with the firmware MQTT client. The topics and payloads are structured according to ONVIF which may be confusing. Also, getting the device to publish events requires additional event configuration.
SIMQTT simplifies device event publishing targeting IT integration. The ACAP includes its own MQTT client and publish events automatically as they occur. You only need to configure the MQTT broker. The topics and payload are simplified. See list of topics & payloads
SIMQTT Legacy is special version that can be installed in all Axis devices prior to firmware 10.0, providing MQTT support for older devices that are no longer upgraded. The main difference to SIMQTT is that it does not support TLS (encrypted) connections to MQTT brokers.
Supported platforms: MIPS, ARMv7hf and AARCH64
Unzip and install the eap-file corresponding to the device platform and firmware version
Additional information on GitHub
ACAP Share 
Have you had a chance to test this with a z-wave hub/router? Thinking about if it would integrate with any 3rd party smart locks on the market now.
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MQTT is MQTT (a messaging protocol). The question is if an MQTT subscriber can be configured to subscribe to a user-defined topic and parse the payload. If a subscriber requires a specific topic and payload, you may need to have some middle-ware client that can subscribe to a topic and republish on a different topic with a different payload structure. Node-RED is perfect for these operations. On the other hand, If you have Node-RED, why not put all the logic and actions there. This is how my home system is designed. A Node-RED in the center, a mosquito MQTT broker, cameras, a Z-wave bridge/sensors, a LoraWan sensors and much more.
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