I’m not a Lutron expert by any means, but I will try to help a bit further.
Yes, your dealer has to come on site to add another account. They should know what you’re referring to when you explain that you want another account besides the default. Make sure they leave the default (lutron/integration) account though, as your Homekit is using it.
The Lutron Connect device is how both Homekit and HA connect to your QS. It’s also how your Lutron app connects.
The last line tho, “Lutron Connect device is how both Homekit and HA connect to your QS” - the Lutron integration in Home Assistant connects to the Lutron processor, at least that is the IP address you give it. So not to say it doesn’t use the Connect, just seems a bit odd.
I will speak to the Lutron installer and try to get him to call in and create me another account.