Yep, that should be fine.
Do you mean adding the free dreamhosters sub-domain and setting it to mirror your domain, as explained in the wiki article I linked above? If that is what you meant, then following that procedure should allow you to access your domain (indirectly) while you are waiting for the DNS to propagate. Personally, I would just wait for the propagation, as it rarely takes more than 24-36 hours (although, it can take up to 72 hours).
I think you will find that since the DNS for the domain will now be handled by the DreamHost name servers, the old re-direction you had will cease to function once the new DNS information has propagated. Any re-direction (if needed) should now be done at the DreamHost end. Although, disabling the old re-direct shouldn’t do any harm.
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