I've been using SU8 for electrowetting for sometime now. I can tell you it definitely degrades over time under water and high electric field. If you want to experiment with it, I guess it would last enough. but If you want to make practical device which lasts for a long (say, more than a month), I don't recommend it.
oh I haven't gone into that detail, since I usually go towards the extreme and almost force my device to break down under very high electric field. that could be a good experiment to do, worth trying and sharing via publication I guess. good luck.