>Does chaining increase the shiny chance?
Yes. We have caught a total of 23 shinies between us all doing this method. I don't have an specific odds, but It definitely increases the odds.
Reddit (source below)
But it's like chain fishing in the sense that you're never 100% guaranteed a shiny. You just increase your chances of finding one.
Pokeradar is more reliable, because we know that at chain 40 your chance of a shiny is at the highest point it can be, so you can just keep re-using the radar without entering grass to get a shiny patch. You're still not 100% guaranteed one at chain 40, but you just don't need to keep smashing through grass.
Reddit thread on dexnav chaining