Not unless you give them actual support. They seem very... unable, or unwilling, to take extreme risks to form empires on their own, probably due to how deadly cities are these days.
I sent you a link to my WWI scenario. At the moment I am testing it out. So far it has been a blast. No crashes, but I do have some questions for Gedemon. About team numbers for civs showing up in the VP display on the game interface. The team numbers differ from what they are in worldbuilder, which is rather odd. In any case I'm sure he'll know what to do about that. At least I hope. Other than that though it runs smooth.
Anyway...
While I was playing the British DoWed me and attacked Brussels. If it fell the British could then attack me in Germany. I had no choice, but to save my little ally. First I gifted them and infantry division. This helped some, but they were being bombarded ceaselessly from aircraft and artillery. I could not get open borders with the Dutch or French. They both hated me. The great thing was they were at odds with each other. Therefore, I invaded the Netherlands and turn Amsterdam in two turns. Then I was able to support Brussels better. Although, I was able to give it some air/naval support in the meantime. The point is that the CS was feeble and would have fallen, if not helped. The thing is though Brussels really does not have much room to expand. Its production capacity is quite limited.
Can you gift air units to a CS? And if you can will it use them? I'll send them some Fokker DR1s.
Look at the length of the Golden Age. That must be nice.Here is a picture of the largest CS empire I have seen in a game.
Spoiler :