No, it's really not when you constrain who the possible perpetrators are and consider that they must be long-term, more senior employees. Fraud by higher ranking employees – particularly managers involved in the creation of job descriptions and doing hiring is just not going to be that common.

It certainly isn't going to be common enough that it's worth destroying internal trust and credibility when open (within company) reviews and sufficient internal control mechanisms that didn't include hidden manipulation of candidate hiring could do an equivalent job without reducing the organization's ability to hire stellar candidates (not that I'm biased, given my case, of course =)

I mean, it may well happen, but all sorts of unlikely events may happen and yet would similarly be problematic to keep constant protection for. It's all about the risk/reward analysis and, in this case, I believe you've calculated that incorrectly.