The SnoPark referred to is right next to Hoodoo. Coming off the highway on the access road, the Hoodoo parking lot is to the right and the SnoPark is to the left--close enough to walk to the lifts with boots on, carrying skis.
According to OR DOT, you can use the SnoParks during the summer if you have the winter pass. However, these things are typically deserted during the summer, so I doubt you would be hassled.
FWIW, Hoodoo also rents RV parking spots with Elec hookups during the winter. In the summer you might find one or two staffers hanging about but they're not going to let you park in the lot, and they WILL roust you.
Are you coming from Sisters? Because Sisters is swimming in great boondocking, and the Hoodoo area really doesn't offer all that much. For info on Sisters boondocking, check in at the NFS ranger station, they are very helpful. Sisters also runs a city RV park, a tidy little place that offers free water to RVers in the area.