My home state, I live in the Bend Oregon area, vacation paradise! So many places to see and things to do! RE roads, try
www.tripcheck.com for weather and road updates. Generally, most major mountain passes by May are safely drivable. Trip check is important because May through October is road construction season too, so not just weather and traffic cams but construction alerts can be found there.
Crater Lake doesn't open the rim road until mid june due to snow/ice and elevation. In May however, so much to see and do. Oregon is really 3 states in 1. A narrow small coastal area that runs the length of the state, separated to the east by a small mountain range from the state's main population centers along the I-5 corridor (Portland, Salem, Eugene, Grants Pass, Medford/Ashland), separated to the east by another larger mountain range. Central and Eastern Oregon are more remote and amazing, high desert and plains, geologic formations, rivers and hot springs, etc... Population centers are smaller and towns are more distant from each other the further east you go!
Not sure where in the state you are headed but by May, you generally should be ok over almost all mountain passes. Watch the weather report, May snow in higher passes is not uncommon, but generally not permanent.