It does sound like a publicity stunt, to be honest, and I suspect its 'allowed' because, who, at the end of the day, is accountable for it? The program makers probably hope to up the viewing figures a little if the 'notoriety' of having Mr (whoever he is) involved will increase people's curiosity for an episode or two (or even if it will just net them, and their show, a few more column inches of discussion in the newspapers), and those on the set probably just have to grit their teeth and bear his presence (regardless of whether or not they are professionals who are seething inside at the depths to which the show is stooping to net viewers). If he's only performing the duties of an extra, anyway, all this is fairly by the by in some sense (though, in another sense, it does appear to be the thin end of the wedge, serving to encourage the ever increasing attitude of 'wannabeism' that plagues the modern profession. It would certainly appear that a frightening, and vicious, circle has been created within the industry - not only is acting as a profession increasingly oversubscribed by all manner of serious actors, good, bad and indifferent, and, in truth, more than the industry can support, but the fact that everyone now wants to be 'famous for five minutes' or thinks 'I could have a crack at that' is opening profitable markets to the producers who make ultimate casting decisions. What is better calculated to get everyone watching, talking and tuning in than giving the 'wannabes' the breaks they aspire to, and telling everyone, a la reality TV, 'look, appearing on TV is possible for him. It may be possible for you, too'? Who wants to watch a professional who is well honed in their craft anymore, when, during, say, an interview, they would only remind you how hard they have had to work to achieve what they do? Production attitudes of this sort are truly beginning to reduce a once proud industry to the status of Jim'll Fix It for the masses!).
This would never have been allowable, of course, in the days of a closed shop actors union, but we have not had one of those for twenty years! Perhaps Equity should have more teeth, regardless, and protest this sort of behaviour with some degree of determination - which they appear to be highly reluctant to do, in most cases. I am not quite sure why, as one would have thought that the union should, even in this day and age, still be concerned with such blatant displays of contempt for the skilled work of the acting profession that it purports to represent - but, at heart, there often seems to be a resignedness at play. After all, no-one is accountable to the Union, anymore. It could protest all it liked, and still be ignored (and frequently is, in matters such as e.g. NMW disputes). There is no oversight body watchdog that is demanding program makers only source labour from reputable arenas. There isn't even anything set in stone about what people deserve to be paid for the use of their skills on screen in most cases, other than the fact that they shouldn't work for free if they are doing a contracted job of work (as you might dress the role we are discussing up as a 'competition prize', maybe Mr. Whoever he is won't be paid for his time, either - and may still be grateful for the exposure and the opportunity!).
What we could really do with is mass boycotts or protests about this sort of thing, which might get the greivance per se noticed - but I suspect most actors would still declare that they had no wish to rock the boat over such 'minor' infractions, and consider the sort of part being taken here to be beneath their interest, anyway, and thus, irrelevant.
Still, a wise acting teacher once said that the only qualification one requires for acting is, unfortunately, being able to move and talk at the same time. Naturally, he was the first to point out that good acting only comes through years of application and attention to the craft. But we live in an age when most people aren't they bothered whether the acting's beautiful or not. They tend to be satisfied with the fact that someone can move and walk at the same time. And when you're working at that level of thinking, anyone does as well as the next man or woman!