I feel like I shouldn't, and should just use the Master Ball, what do you think? This is for my Sapphire Nuzlocke for those who don't know.
Don't risk it. There is no point in foolishly trying to catch a powerful legendary with a catch rate of 3, in a Nuzlocke of all things. It's simply too much risk to be worth it, when you can easily catch it with no struggle.
Hope I helped!