I think its fair to say that 99% of people flying an ILS expect total protection on an ILS approach, it matters not that the conditions are visual or IMC you are flying a PA.
If the 402 was cleared for the ILS then there should have been no conflicting traffic period
I think they key here is that the Cessna, ILS or not, was on a
VFR flight as far as ATC were concerned.
An inbound 737 would have been IFR all the way down to the runway and would have received IFR separation (from participating traffic only, obviously, this being Class G).