Are their differences in a DUI for drugs and a DUI for alcohol?

Yes, but they depend on the type of drug. A DUI for a "soft drug" such as marijuana is going to be completely different than a DUI for a "hard drug" such as Meth. The difference is in how much the drug will impair your driving. Small amount of marijuana, for example, have been shown to only have minor affects on drivers.

Below is an article on DUI on marijuana and one for DUI for methamphetamine.