I first noticed 'them' being used instead of 'those' way back in the 1980s when I was interviewing applicants for a junior office position. Unfortunately this was only the start
But 'them' for 'those' isn't exactly a new or modern usage. It's been around since long before you were born as part of the everyday speech of most of northern England; I believe in some parts of the country they prefer 'they'.
What may be new-fangled here is someone using a regional term or a colloquialism in a fairly formal situation. I tend to agree that different settings may call for different ways of speaking, but it might not be an applicant's fault if they have never learned many of these. Shouldn't it rather be celebrated that (a) an ancient usage of these islands has been preserved, and (b) someone feels able to apply for office work in spite of not knowing how to talk proper? Rejecting someone because they don't speak King's (or Queen's) English could lead to all kinds of issues...