Why do they need to hold Brigade officer status to attend the one off incident ? They can still be volunteers and be a resource to the incident if required.
If they are a Brigade/Unit Officer & part of the management group of the Brigade/Unit. How can they argue properly for your better truck, equipment, funding, training, etc that your volunteers need in the Brigade, when they are arguing with the person who could affect their employment (now or in the future) ?
Personally I believe all paid staff should drop volunteer rank. They can be a local resource to the incident team and brigade with speciality expertise (like any other builder, plumber, farmer, electrician, etc).
The reason I say all paid staff, is that at a major incident many of the 'non operational' staff are used (eg VSO cars provide crew transport at a major inicdent, secretaries answer telephones, etc).
So then your Brigade/Unit Officer is not available to the Brigade, so you are missing part of the Brigade structure & a important resource at a major incident.
You are then trusting your non-officer volunteers to manage the Brigade at the incident. If you trust the volunteer that much at the incident to be the officer, then trust them to be the officer every day.
** My personal opinion only **