I use silk plants in one of my tanks and a fake square of grass (all bought at Michael's) and they all are fine. I've had no adverse effects on my water chemistry or fish behavior. In fact, they don't show any preference towards those plants any more than any other fake plant in the tank. The grass thing that I used is in this video (I bought the silk plants later). [video=youtube;QwP68sQq-M4]http://www.youtube.com/watch?v=QwP68sQq-M4[/video]
But I just made sure to rinse it off really well under cold water and then I let it soak for like 1-2 days in just a bucket of water and changed the water 2x day. It worked great as a little hideout for my kirbensis fry when they were still super tiny.