I really wouldn't sweat it. I've made starters with and without foam control, you add it to mostly control boil over in the flask on the stovetop, not really for when it's on the stir plate. But it helps a bit there too.
I think I've had one foam over on the plate. Happened when I was at work with a very active starter filled to 2L. Just a bit of yeasty foam crud down the flask and on the plate, no biggie. It's not like a boil over where you can loose a large qty of liquid. At least this is my exp.
Check out my homemade stir plate here: newenglandhomebrew.com, just wrote a post on how I put it together. I have a video here of a wlp007 starter going to town. This is a crazy yeast, almost looks like cheese curds or something it's so flocculant. Anyway, this was with foam control and you can see how active it is with little foam.