I'm not expert but I would think it would be fine and they'd love it. Celery is pretty harmless stuff and it is not on the "DO NOT FEED" list. I would go for it, but maybe wait until you get a few more responses from other people. If it were mine, I wouldn't hesitate.
There are very, very few exceptions to the general principle of "if it's good for you it's good for the chickens too". (Main exception, which isn't *really* an exception, is that people can tolerate quite a lot more saltiness before succumbing to kidney failure than chickens can, so salty foods are not good for chickens even if *you* like 'em).