There can be a problem, but it depends on your sites. They say they'll work with you. If you have some information on how resource intensive the sites will be, you could always talk it over with Support or Sales.
They hired more support help.
Tip me (and DreamHost gets 5%+$0.30) Cut the code: [color=#00CC00][b]9999[/b][/color]=$99.99 Off