Yes, IF you had created an enforcement relation, then you could have put the camera at its actual position as the device.

If you ONLY tage the camera, then it MUST be on the road, see: https://wiki.openstreetmap.org/wiki/FR:Tag:highway%3Dspeed_camera

If you only tag a speed_camera that is not on a way and not member of an enforcement relation, then it is useless. Consumers will not use it because it is an error.