yes, the onsite hotels have shuttles and a guest would sign up in the hotel lobby the night prior to reserve their seat on the shuttle bus to SW from there.
I have only seen the morning shuttle to SW schedules of one or two time periods in the morning.
there is a return shuttle near the end of the park day of SW
how many shuttles, don't know for sure.
from what i have read, there are no assigned seats for that return shuttle, more of a "first come, first served" set up.
check with UO to find out if SW shuttles are available from the parking garage.
with increased visitors to all the parks, i would think there would be more.
i think the flex pass would work fine for free parking.