The problem that I have with the idea of taking a pay cut to save fellow officer's jobs is that there is so much waste in most city/county/ state budgets. In lean budget times, government should be cutting back in areas that are luxuries, or where there is duplication of services. If police unions don't fight against pay cuts, furloughs, and staff reductions, this waste is tacitly encouraged to continue.
I would be hard pressed to agree to a pay cut if my employer still had a 'Diversity Coordinator' or a 'Human Rights Director' still on staff. At best, such positions are luxuries. At worst, they are completely unnecessary. They should go before any positions in the essential services of law enforcement, fire service, or EMS.
Before accepting a pay cut to prevent staff reductions, I would press the union to mount a fierce PR campaign against any such moves. But in the end, my co-workers are family, even the newest guys and gals. And if push came to shove, I would probably agree to the pay cut if I knew it would save their jobs. Sadly though, I think most government managers know that most of us feel this way and will use that to break our will.