DreamHost basically allows you to host whatever you like, as long as it complies with the laws of the United States.
If you own the copyright for the ROMs, or have permission from the legitimate copyright holders, then you should be OK.
Having said this, for an authoritive answer to your question you should contact DreamHost using the form linked below;
Edit: wow! simultaneous posts
Save [color=#CC0000]$50[/color] on DreamHost hosting using promo code [color=#CC0000]SAVEMONEY[/color] ( Click for promo code details )