Well, to my knowledge I don't think dreamhost blocks port 22 or any other port. OTOH, there are services that dreamhost is already running on your server that use certain ports - ssh, telnet, apache, ftp, etc, that you "can't" really override except via the acceptable mechanisms - proxying, for instance.
FWIW, dreamhost support is always happy to answer your support questions - except occasionally for specific questions about fraud detection (for obvious reasons). Plus we have a very active user community that can answer many of your questions (and which you yourself can contribute to). This community is active both here on the forums and over on the dreamhost wiki. You do have to pay extra for phone support, though.
As I said, my understanding is that they'll let you use any TCP port that isn't already being used.
One other thing that's important for you to know is that DreamHost PS isn't exactly the same as a VPS. It's still a managed hosting service in that they provide a control panel and a number of pre-installed services. No one who's posted here has tried to override any of these services so we don't know whether they are overridable. The good thing is that you get a lot of functionality that works right out of the box while still maintaining the capability to SSH into your server and install other applications and servers as you need them. Oh, and also remember that you don't get root access on DreamHost PS.
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