Are they possible?
I personally believe they aren't because if you are working to eliminate the state, you can't be working for it.
But then again, if I went and joined the police right now, and worked to dismantle the state within the police department then I could theoretically be a Anarchist copper.



Can comment on articles and discussions
It's something (that I'm rather loathe to admit) I've considered at various points...
IMHO, since I think it would take about 20 years of being a committed and serious anarchist not to have one's beliefs jeopardized by participating in such an institution (and about that long to have built enough trust with comrades that they would work with you whilst inside such an institution... you'd want to be able to share information gleaned from the inside wouldn't you?), it becomes something of a non-issue as at that point you're too old to join most copper academies anyways.
Like the military they prefer their recruits be young and brain-washable (and I suppose more physically able... most fire departments don't take people over 35 either).
trivia: the first Anarchist Free School in Britain was founded by a policeman (but that was a cop infiltrating anarchists, not the vice versa you propose).
*Edit*- not really what you are asking about but another sketchy job option I've considered is that of a civilian oversight board investigator... which only some citys operate (basically the lame paid official government version of doing copwatch ... interviewing complainants and officers, etc. )