I’m passing MQTT messages bidirectionally between HA and both Particle Photons and Particle Xenons. I’ll be glad to share code, but let’s not do it here. You can message @Bear to reach me in the Particle Community.
I had done this quite some time ago now, but I have as of about two years ago cut the blinds over to a basic esp8266 chip with mqtt. I also have my theater lights still on particle photons with curl statements, I can try to pay that code for you if you are interested.
I think it is appropriate to share Particle code via the Particle Community so other Particle developers can benefit and/or chime in to help. Likewise, I think it is appropriate to discuss HA related issues on this site for the same reason.