I actually find that her top ganks are easier when playing on purple side because of the placement of that wall at the end of river, which you can come up to and tunnel under to basically put yourself all the way in the lane as opposed to the blue side top river wall where you tunnel through and only get to that bush and have to walk the rest of the way to the lane. But that's just me.
As for the rest I can kinda see what you're going for, but it's no more than any other jungler has an advantage on with dragon. And even then it's not a matter of who has a better chance with the dragon fight, just that blue side has a slightly better access point. However remember that if blue side aren't playing champions who can hop over that wall they have to go a bit out of their way to first walk around the pit and then through river a few steps to the relatively small entryway, whereas purple side can rush straight down from their blue buff and crowd into the dragon pit in one straight line. So while blue has slightly easier access to warding it, their entry isn't necessarily as easy especially when lacking mobility options that can get over the wall. And just because Rek'Sai can doesn't mean her other teammates can as well.