Yes. All the DreamHost shared hosting plans allow you to create many machine users with FTP/SSH access. The numbers for the various plan levels are shown below;
L1 = 75 users.
L2 = 175 users.
L3 = 375 users.
L4 = 775 users.
Yes. Each database exists on a separate subdomain determined by you at the time of creation.
You can access phpMyAdmin using the URL for that sub-domain (http://mydatabase.mydomain.com).
Save [color=#CC0000]$50[/color] on DreamHost hosting using promo code [color=#CC0000]SAVEFIFTY[/color] ( Click for details )