Well, you can do it that way, although you'll find it much more convenient to use Dreamhost's nameservers for the domains that you want to host here.
You can do what you say - add the hosting here at dreamhost, look up the IP address that gets assigned to the domain, and put that as the A record for that domain. If you're going to use the phpmyadmin for mysql, you'll need to add that A record as well. Basically, you need to make sure that you add A records that match all the subdomain records that get set up for the domain at Dreamhost. You also need to make sure they stay in sync if the IP addresses change at Dreamhost. They don't change that often, but it's still just another thing to worry about keeping in sync.
Speaking of keeping these things in sync, you should realize that keeping DNS records in sync is what the whole DNS system is set up to do automatically.
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