They stack with the others, i think at 1% health you get 60% resist to all with the 3 passive sets. 40% with the 2 passive sets.
Add in resist IOs and tough and you do fine. Generally you get tagged into the red, but then the other hits never come and you regen back to the green.
My SR tanker is nigh unkillable and I never got aid self or anything. SR brute is decent also.
SR scrapper is really good after level 35, but before that you will get hurt a lot by AOEs.
You have to run tough though since the set has no place to slot the 3% defense global IOs
Some nice perks is you are immune to defense debuffs, and slows rarely affect you.
Sent SR has a end recovery bonus, so has some added utility.