Answer to "Is it safe to unplug rinsing dispenser from dishwasher?"I don’t see this as a problem. All your doing is bi-passing the dispenser. Be sure to tape the ends of the wires. Especially if your disconnecting from inside the lid. Remember the lid has movement causing the wires to shake. If one should get in contact with a conductor it will cause a short. Tape it tight.
Answer to "Should there be any standing water left in the sump?"You were right the first time. If you have standing water below the filters your fine. That is normal to keep seals from drying out. Water above filter line is a problem.