Vegetables usually like alkaline soil and sun which would not be good for camellias that prefer somewhat acidic soil and partial shade.

Camellias generally do not have very extensive root systems when compared to their growth above ground- the exception to this rule is if the soil they're in is not kept consistently moist/mulched, and then the roots may travel out to seek water.

Since the roots are fairly close to the surface, you could probably find out how far the root system extends by gently digging/raking around the plant to see where the roots end. Just be sure to water the plant after you're done and recover with soil and mulch to prevent moisture loss.

Because those roots are close to the surface, you're quite right to be concerned about smothering them. How close were you thinking of having your raised bed?

restoner does raise a valid point about lighting- vegetables generally prefer more light than camellias, but this may not be an issue if your camellia is well-established in a reasonably sunny location, or if the planned bed just happens to get more light than the camellia. As for pH, there may be some veggies that prefer a 'sweeter' soil, but many will tolerate/ thrive in an acidic environment. And if it's a raised bed with a weed barrier, I don't know that there's much of an issue with your camellia suddenly having to cope with more alkaline soil?

The issue of lighting seems more important- trust me that it's hard to raise veggies in shade- I've tried!