Crabs and snails will munch on the shaving brush too. Many different fish will make quick work of the plants. Although I never noticed my flame angel eating the shaving brush, i have never had success in keeping them for very long. Multiple creatures chew on them, and they're not too hardy in the first place.
Also, claims that shaving brush plants reduce nitrates are a bit overexaggerated. They do help with nitrates, but I've never noticed them helping enough to warrant continual purchase.
So, the answer the your question I guess is I'm not 100% sure. My angel never really touched the plant, that I saw at least. But I know most of my other species liked chewing on the shaving brush.