Cloudflare's proxy is only for HTTP Traffic. They're not assigning you a Unique IP or anything, so without something like Cloudflare Spectrum they'd have no way to tell what arbitary tcp traffic is for your zone vs someone elses.
I wouldn't use it for heavy traffic or something mission critical imo as you are adding another layer and as far as I know, that was designed more for client to site connections then point to point/server to server. People have used it in the past though