I was reading that tubeless sealant might contaminate the pure nitrogen, so you won't really benefit from the longevity it'll provide from pressure loss. There's also the possibility the sealant won't react properly sealing punctures since there's less oxygen in the tires. Though I'm no chemist, so for all I know everything I read was just BS and it'll work great!
Though if you can get free nitrogen at Costco and the container only cost like $35 USD, I'd get it as a cheap way to have pressurized gas for beading tires. I'm too cheap to get a compressor so I usually just bead my tires at the gas station pump.