The point of the Simic guild is to 'build the perfect creature'. This works best if you start from a very good creature -- like Simic Sky Swallower, say. Or, in this case, Phytohydra.
Phytohydras are a lot happier when they can block flyers (aquastrand spider), untap after attacking (vigean graftmage), or can't be the target of spells or abilities (plaxcaster frogling). And when they come into play as something bigger than a 1/1. On the flipside, Vigean Hydropon is a quite effective secondary holder of a pariah's shield. Especially if it's regenerating (sporeback troll).
I also put in the 'remove a +1/+1 counter to get two 1/1 flying spirits' guy, since he seems tailor made for Simic (with Simic he starts with +1/+1 counters and his spirits can be bigger than 1/1) and I was already adding white for Phytohydra.
That said, it probably won't be as effective as the red phytohydra deck until it's tuned a bit more, and maybe I get some more cards... in particular more plaxcaster froglings, which I already ordered but haven't come in yet.
I've also discovered that Experiment Kraj is a failure. It really doesn't work well with most Simic decks, since for its primary ability to be useful (it gets the activated abilities of any creature with a +1/+1 counter) it needs to be copying abilities that either only affect the creature that has them, or require tapping. So, Simic Ragworm + Minister of Impediments + Experiment Kraj == Yay, but none of those belong in a graft-based deck.