Am I allowed to park my domains with services such as Sedo, to generate revenue whilst I am still working on content to publish to those domains? Does this violate any rules of DH?
I'm not a DreamHost rep, but you can park your domain anywhere you darned well please. Once you start hosting your domain here is when you need to be concerned about DreamHost policies.
I confirm what @sdayman said: you can park your domain at Sedo, no problem