CloudFlare and externally hosted site

I’m using DNS only, hosting a couple specific subdomains but have my A record pointed to a third party host. Can I still use the DreamHost CloudFlare offering? Any caveats?

No. DreamHost’s CloudFlare support only works for sites hosted on our servers. If you want to enable CloudFlare for sites that you have hosted elsewhere, you will need to do that through CloudFlare directly.