I see no reason why such participation would be a threat to the employer or cause for discipline. Proprietary information can be inappropriately shared in any forum on any subject whether directly related to the purpose of that forum or not - every person would therefore have to cease participation in any public discussion to avoid "accidental" sharing; what is required is simple responsibility. While open participation by airline employees is relatively rare, there certainly is some history here as well on other air travel discussion forums, in at least one case, a commercial airline pilot is a moderator.