Few more thought to add to what Thing2 said.
We used Pacenti SL23 rims, stans tape, and Orange sealant. Other than issues with longevity on the rims (got the 2015 edition on order as a replacement, will see if that fares better) I was pretty happy with this combination.
A challenge for tandems is if you get a puncture that seals, you have a greater chance of blowing it out when you reinflate, compared to a half-bike, as you'll probably be reinflating to a higher pressure.
With the exception of the Fusion 3, the tyres we had cuts in were all still usable with a tube inserted. The issue is this feels like you're missing the benefit of tubeless so we tended to replace them sooner than we would have otherwise. Combined with the higher price, this is what made it an expensive endeavour.
At the USA nationals last year, several (fast) tandems were racing on tubeless and where the envy of those that weren't. I'll try and find out more about which tyres they used.
We've not yet tried the Hutchinson Sector 28. Sounds like we'd be pushed to fit that in our frame.