I discovered the root of my own problems and its tied to Control4's home/account management and the way their driver "handshakes" with homes in Homekit. Here's a quick run-through for anyone troubleshooting this in the future:
We have a city home and a vacation home: 2 homes in HomeKit, 2 homes in Control4
HomeKit setup is using my own personal iCloud account (1 email address: emailA), its the primary account to admin the homes in HomeKit. The homes are shared with multiple family members.
The two homes in Control4 each require a unique email addresses. City home account was created with emailA, and for the vacation home account I created an email alias, emailB.
When adding control4 to HomeKit at the vacation home, I received the dreaded "Unable to complete Apple TV integration" error and spent the last few weeks troubleshooting. And after some digging I've discovered the following:
The email address registered to the home in Control4 has to match the email address used in HomeKit. In my situation our vacation home was using emailB, and HomeKit is managed using emailA. Control4 explained to my integrator that this was the issue and there is no way around this.
I spent a few days thinking about ways that I could create some dummy accounts to get by this limitation. I could create a new appleID, emailC, and share my vacation home in HomeKit with emailC, then create a control4 account using emailC and add them to the house, and try to complete the HomeKit integration (can't guarantee that this would work, but I was willing to give it a try). I didn't get very far with this option as Apple only allows 1 phone number to be registered to an AppleID at a time and surprisingly we don't have another unused phone number. I started looking into dummy phone number services, but thought I was going down a real fragile rabbit hole creating dummy phone numbers for dummy email addresses.
At the end I gave up on Control4's solution and installed the @IntrinsicGroup IP driver, but sadly it doesn't have the long press on the TV button to bring up tvOS Control Center and all 4 family members use their AppleTV accounts to track their watch history across all our AppleTV's. But at least there is a "long route" to switch users in the settings app, and that will have to do until we get long press support in the @IntrinsicGroup driver. Fingers crossed!
A potential solution for the root problem would be if Control4 allowed a single email address to be associated to multiple homes. Then emailA would be registered for both houses and we wouldn't have the issue. That would be swell. Is there a feature request voting system somewhere? I'd smash that upvote button.
So there ya have it. Happy to answer any questions, and hopefully this helps someone else out.