I would say it's probably quite safe - one can spray or soak orchids in regular dishwashing detergent as long as it is properly diluted. Two cautions - 1) don't spray the leaves and put it anywhere in direct light - sunburn, etc., and 2) good luck getting rid of mealybugs with anything eco-friendly! I tried everything, incuding rubbing alcohol, finally ended up with a chemical insecticide, and once the mealybugs finally succumbed, the plant had, too. I tossed it just in case there were any of those nasty things still left - it's the only mealybug-infestation I have ever had, and I'm not looking forward to any other ones - they're pretty awful, so don't play around too much. One of your best bets might be to unpot the plant(s), soak them for an hour or so in a dilution of detergent and insecticide, then repot them in new media. As long as you don't have any bloooms or buds on them, soak the whole plant - those things hide under everything. You may still end up having to toss the infected ones - it's not worth subjecting your other orchids to potential infestation. Oh, and I'd think that if you see mealybugs n the bark, they're already hiding in their favorite places on the plant as well.
I sympathize. Good luck!