I've got this working pretty well now as well. All of my zigbee and z-wave devices are paired with the hubitat, but my automations are in appDaemon on HA. It really works! My experience so far is that it's both stable and fast, and I'm just running hass.io on a VirtualBox.
I wish I had an identical app running locally in groovy to do an apples to apples comparison to my appDaemon python apps for speed, but it seems pretty damn quick to me. Makes me wonder how much of the slowness/weirdness I was seeing on SmartThings with WebCoRE was coming from WebCoRE.
At some point I intend to look into re-writing the MQTT app for Hubitat. First off, it shouldn't need the broker component as ported from SmartThings since your hubitat and mosquitto server are probably behind the same firewall.
Second feature I'd like to add is creation of the topic names in such a way that HA will auto-populate discovered devices. Looking at the HA docs, this doesn't seem to be too much of a stretch.
Final feature would be ssl support on the HE side. Not sure exactly what would be involved in that.
Maybe over the xmas break...
Oh... as for the mqtt broker component, I packaged it up as a hass.io add-on if anybody's interested:
Configs to get it working with mosquitto look like this:
-------------------
Mosquitto config
cut below
-------------------
{
"logins": [
{
"username": "myuser",
"password": "mypass"
}
],
"anonymous": true,
"customize": {
"active": false,
"folder": "mosquitto"
},
"certfile": "fullchain.pem",
"keyfile": "privkey.pem"
}
--------------------------
hubitat bridge config
cut below
--------------------------
{
"broker_host": "localhost",
"broker_port": 1883,
"preface": "hubitat",
"state_suffix": "state",
"command_suffix": "cmd",
"login": "myuser",
"password": "mypass",
"bridge_port": 2081
}