That’s an apples-to-oranges comparison; qmail is an MTA (put simply, mail server) and Mailman is a mailing list application. One has nothing to do with the other. You can’t install your own mail server software on a shared hosting service. Dreamhost does not use qmail, so ezmlm cannot be used here.
Mailman isn’t great, but it’s probably the best free mailing list software available (a sad state of affairs). I haven’t used ezmlm, but the fact that it requires qmail pretty much automatically puts it below Mailman, regardless of its actual capabilities.
If you want useful replies, ask smart questions.