Typically yes, those without seats are the first bumped. My understanding is that those with seats get them, at 10 minutes before flight, those not checked in and at the gate, are assigned the seats that were previously assigned. Seats assigned at the gate are assigned based on your status and what time you checked in.

It is rare for an SE/E to get bumped, rather they will "off-load" the non-status individual so as to keep their most frequent flier happy.