I had the same dilemma, and I ended up with the exact same solution as you. I literally just came here to check to see if there was a better way of doing it when I stumbled upon this thread.
I have a scene called "All Kitchen Lights" that controls the kitchen lights, foyer lights, and island lights. The controller for the scene is a keypad button, and just like you, I only wanted the button to light up when all three sets of lights were on. The only way I could come up with for accomplishing this was to create a new scene with only the keypad button in it, and then trigger that scene from a program:
All Kitchen Lights Button Monitor - [ID 000B][Parent 0001]
If
'Main Floor / Kitchen Lights #1' Status is 100%
And 'Main Floor / Foyer Lights #1' Status is 100%
And 'Main Floor / Island Lights' Status is 100%
Then
Set 'Main Floor / All Kitchen Lights' On
Else
Set 'Main Floor / Keypad (B) Status Control' Off
It works like a charm! I guess great minds think alike!