I can not say with a certainty if they could find out your real server’s IP address but even if they do, you should not worry about this as long as you do not do some blackhat stuff on your websites. I use the CloudFlare service as well and link some websites to each other (but not all) and I have not had any big issues with Google. You can create many CloudFlare accounts for free so you will use different name servers and IPs and this will decrease chances of getting caught by the big G.