First off, dwarfs need to be kept in a small tank because they need dense live enriched food, usually enriched ongrown bbs to feed from, and the remaining food needs to be removed before next feeding.
Second, with just a pair, it will be hard to see them a lot of the time.
As for kuda or any standard seahorse, it is misinformation that they need only slow flow when in fact they can take slow, medium and high flow areas as long as there is hitching in each area and as long as the high flow can't blast them against something to injure themselves.
Mixing species is NOT recommended as it often leads to the demise of one or both species due to exposures to pathogens they haven't experienced growing up.
Mixing dwarfs with kuda especially is bad also because of their very different feeding methods as kuda, while fry size will feed of bbs, will ignore them as they get larger but the dwarfs will not/can not eat the frozen mysis that the kuda feed on.
Life span of dwarfs IS short, typically about 1 1/2 yrs with some getting to around 2 yrs old, possibly a touch more under ideal conditions.
Standard seahorses kept in ideal conditions can live 5 to 10 years but many don't make it even a year, some due to lack of knowledge, some due to lazy husbandry over time, and some due to unknown factors.
From your wanting to keep kuda in a jellyfish tank, I suspect you haven't the best source of information on the seahorse hobby yet.
There are links at the bottom of "
My Thoughts on Seahorse Keeping" written by experienced keepers and a commercial breeder that can give you a better insight into the hobby.