No sealant on exhaust pipes. It gets too hot. Sometimes you might see a 'tin' gasket...like a thin metal thing. But not right there. As the other folks said, it's a press fit and the cone inner collar slides up into the chamfered hole on the inside of the flange and the tightness of everything makes it not leak.

As a sanity check, you can leak test it yourself. At the mechanic shops, they have a smoke machine that makes a harmless smoke you place around air fittings like that with the engine running and look for bursts of air(the leak) pushing the smoke away. You could do the same thing in your garage...even if you don't have a fancy smoke machine. Maybe some incese and a hair dryer duct-taped to your exhaust pipe? Get creative. Anyone walking in will think you're having a hippie smoke out...but you'll know better ;D

I would align it right(even) before tightening it up. Usually, people just wrench tighter on the bolts to eliminate the leak. But, you want to make sure the tightness on the bolts is coming from actually scrunched down and not just friction from being misaligned. You might think you're tightening it, but you're not even close and the bolts just snap on you. So, loosen everything up(all the way back, so you can freely wiggle) and just bolt it up without anything limiting you. After that, you can strap the pipes down with the hardware. It's easier to leverage an installed pipe closer to a hanger than line up threads on a Flange fitting. This works on fixed brake lines and fuel lines, too. Forget trying to get a fitting aligned with no room for movement!