In reply to:
If I move my website and e-mail to Dreamhost from CoreComm, would there be any problems in e-mailing?
To properly answer that question, we would need to know a good deal more about what you mean by "problems" and exactly how you intend to use your email on Dreamhost. This is primarily because of Dreamhost's smtp/sendmail limits and quotas and things like ISP port blocking that could mean you would need to reconfigure you POP/IMAP clients to use an alternate port. If you consider email associated with the domain in question to be "mission critical", I suggest you search these forums and read up a bit. Given the nature of "shared server" hosting, some Dreamhost users have found it desireable to host their domain at Dreamhost and their email at a dedicated email service provider. Here, YMMV, but it never hurts to research a bit ;-)
In reply to:
For instance, if I had an account email@website.com with CoreComm and I wanted to have that same e-mail account with Dreamhost (at my own domain of course), could I just create that same exact e-mail account after I move the nameservers over?
The answer to this one is a lot more straight-forward, and the answer is "Absolutely, Yes!"
--rlparker