The TOS say 1 account per person, or termination of both.
In reply to:
The Customer agrees to hold only one (1) active web hosting service plan at any given time with DreamHost Web Hosting. Signing up for multiple plans is grounds for termination of all plans, including the first one, without warning.
While this isn't likely to be enforced if you have two lightly used accounts, for the purpose of keeping them separate... I'd guess they're not going to let people pin resources on multiple accounts... if they catch it.
The reason they can offer that much is because most people don't use it and it pays for those that do.
Dedicated hosts do the same thing when you try to add another 1,000 GB of bandwidth to a dedicated server. It ends up being cheaper to order multiple dedicated servers than adding resources to one.
The good part is that a dedicated server company isn't going to tell you to not keep buying servers, but doing the same in a shared environment affects other users.
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