It sounds like you have great number of visitors of your website. I’ve not heard of anything about CPU quota in DH. But all the computers have CPU limits. The CPU can’t run beyond that. If your site consume too much resource in shared server, it will definitely affect the performance.
You can check DH’s new feature http://wiki.dreamhost.com/DreamHost_PS Maybe it will help you a bit with your problem.
For you domain, you can either host it or transfer the registration. If you just host it, the domain is still registered with bluehost. You pay to bluehost to renew your domain.
If you transfer the domain to DH, the registration of domain will be transfered to DH. It will be then registered with DH. You pay to DH to renew your domain.
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