My opinion is it's a bad idea.
1. Carpet anemones get BIG.
2. Yes, there is always the chance that it would eat a fish that blundered into it.
3. Keeping one alive for a year means absolutely nothing considering they seem to be nearly immortal in the wild. I'm sure having it under PC lights and supplement feeding it could prolong it's life over plain flourescents and no food but in the end I think it would've died from lack of light.
4. You can place an anemone anywhere you like in a tank, it doesn't mean it's going to stay there, so you can't guarantee in any way how far away from the light it will be.