Yes, you can do that.
You do have to add the domain to your DreamHost account, then add the subdomains. You do this through the "Domains>Manage Domains" section of the control panel. The "button" is "Add New Domain / Sub-Domain".
After you've added the subdomains, go back to the "Domains>Manage Domains" page. The subdomains you created should be listed there in the table. For each one, click on the "DNS" link. This will give you the DNS information for that subdomain. All you really need here is the IP address. With that, you can manually add A records at your other host.
For completeness, you should "delete" hosting for the main domain.
Finally, you should note that there are rare occasions when the IP address for a domain or sub-domain changes. In that case, you will have to manually change the DNS records at your other host.
Note that these instructions are for people with regular shared accounts. If you have a dedicated or private server, it is somewhat simpler.
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