It seems to me the tactical advantage they'd have would be first and foremost knowledge of the terrain.
If they've been mucking about there as nomads for a while, they'll have learned where the (and I'm guessing at wildlife, so please allow for these being examples) 'gators hang out, where the birds nest, how to watch for water moccasins, and what to put on their skin (and how to dress) to keep the bugs off. They'll also know where the sinkholes and quicksand (or fast-acting equivalent) is, where the water flows with an actual current, how to find stable land, and where to find or how to scavenge for food.
This is going to be key to any battle, especially a lengthy one. On one side you're looking at an army--likely armored, which is the worst thing you can wear in a swamp--eaten up by bugs, possibly falling ill from bad water or the viruses the bugs may carry, being picked off by dangerous critters that hide in the water, and sooner or later running low on rations. On the other you have the natives, well able to booby trap their swamp, adept in knowing where to step and how to survive, well fed, often well rested, and able to vanish when the going gets rough.
Even if the attackers are technologically superior, the nomads have more than a fighting chance at winning, especially if they hit them with guerilla warfare instead of a head-on confrontation.
Of course, the easiest adaptation for using a method others can't might just be swinging on well placed vines or ropes--it takes practice to use those right and not whack into a tree. Rope bridges way high up are also a time-honored form of transit and ambush, so long as they're hung well out of the reach of saboteurs.