Yes, it is possible to draft against specific ADP or pre-draft rankings.
When you are on the Draft Simulator's Draft Settings page, scroll down to the Draft Against section. Here you can select whether you want to draft against expert rankings, a variety of ADP sources and/or pre-draft rankings. You can select any combination of ADP sources and pre-draft rankings you want to draft against.
It isn't possible to draft against specific expert rankings, but you can toggle on/off the "Experts" option depending on whether or not you want to draft against a random set of expert rankings.